I've been wondering, between Fate/Zero, Fate/Stay Night Realta Nua, Fate/Stay Night (anime), Unlimited Blade Works (movie), Fate/Extra, Fate/Extra CCC and Fate/kaleid liner PRISMA☆ILLYA (and to an extent Carnival Phantasm), have the same Japanese voice actors been employed for returning characters (e.g. Saber-Arturia, Gilgamesh, Rin, Ilya, EMIYA)?
Also, if they have remained the same, is there any confirmation that Fate/Hollow Ataraxia on the PS Vita will follow the same trend?
This will only be a partial answer addressing some of the major characters, because there's too many characters in the Fate universe for me to be bothered tracking all of them down. Broadly, though, with the exception of male characters like Shirou and Kiritsugu who are played by women when children and by men when adults, I know of only one case in which different VAs have played the same character in different entries in the Fate-universe.
This one case is that of Sapphire in Prisma Illya. The unfortunate passing of Matsuki Miyu after the airing of 2wei Herz led to her being replaced by Kakazu Yumi in 3rei.
Re: Fate/stay night - the casts of the 2006 anime, the UBW movie, Realta Nua, and the 2014 anime are all the same, at least for the major characters, so I haven't specifically made a note of that in the list below.
This Crunchyroll article lists some of the voice actors for the Vita port of F/HA; all the ones that are listed are the same people that played those characters in earlier Fate entries. The Japanese Wikipedia article for F/HA also lists some more VAs for F/HA, citing Type-Moon ACE Vol. 9; all of these match up correctly too.
Besides, I don't think it would be in Type-Moon's best interest to change VAs for any of the major characters - imagine what a fit fans would throw if their waifu/husbando got a new VA!
You didn't ask about Tsukihime, but do note that the voice actors for Tsukihime in the 2003 anime all differ from their voice actors in Carnival Phantasm. If the Tsukihime remake ever happens, I suspect that they'll stick with the Carnival Phantasm VAs rather than the 2003 anime VAs.
(Very late answer, I know, but I wanted to say this anyways) Well, this might take a while, so get ready:
As far as Fate is concerned, it's voice cast has surprisingly consistent ever since the 2006 anime... with the shining exception of Bediviere. The guy has gone through (I kid you not) 4 different voice actors. The first was Mamiko Noto in the 2006 anime, then in the PS2 version of Realta Nua Shinichiro Miki (Assassin's VA) took up the role, then in the PS Vita version of Realta Nua, the role was passed on to Mitsuaki Madono (Issei's VA) and finally, in Fate Grand Order the role was passed once again, this time to Mamoru Miyano, and it'll hopefully stay consistent from now on.
There are only two other characters who have changed VAs as far as I can tell. The first is Kuzuki, who is... a bit harder to explain. Basically, for all of the Studio DEEN productions, the PS2 Version of Realta Nua and Carnival Phantasm he was definitely voiced by Kazuhiro Nakata. I also know for a fact that in the second UBW adaptation, the PS Vita version of Hollow Ataraxia and the Heaven's Feel movies he was voiced by Masaki Terasoma instead. Finally, I am also aware of the fact that the late great Unsho Ishizuka voiced him in Unlimited Codes and the Tiger Colisseum series. However I have no idea on whether Nakata or Terasoma voiced him in Emiya-San or the PS Vita version of Realta Nua. I'm gonna throw a gamble and say it was Terasoma for the sake of consistency, but don't quote me on that.
Finally is the matter of Luvia. She's voiced by Yukari Tamura in Realta Nua and Shizuka Ito in everything else. I know, surprisingly easy to explain, right?
Aside from that, Fate's cast has actually stayed very consistent thought.
As for Tsukihime, well, I don't think I even need to mention the mass recast that was done for the Melty Blood games and how we're now stuck with them. The only character to note is Hisui. As a result of Miyu Matsuki's passing, the role has returned to Yumi Kakazu, who had previously voiced her in the anime that does not exist.
I do however wonder what they'll do with Capslock-Kun. He hasn't had a voiced apparence in a while, so I don't know if they'll recast him or they actually decide to bring Hiroyuki Yoshino back (Which woudln't be that bad of an idea. I mean, Yoshino flat out sucked as Roa, but I actually think he could pull Capslock-Kun off). The former is far more likely, but who knows (And if they do recast him, they better bring in Nobuhiko Okamoto).
Finally is the Kara No Kyoukai cast, which is thankfully easy to explain. From what I've been able to gatter, all of the cast used in Drama CDs previous to the movies' release was different. It was more along the lines of this:
The late great Tomoko Kawakami as Shiki (Passed on to Maaya Sakamoto).
Kentaro Ito as Mikiya (Passed on to Kenichi Suzumura).
Kikuko Inoue as Touko (Passed on to Takako Honda).
Yukari Tamura as Azaka (Passed on to Ayumi Fujiwara).
And finally, Miki Ito as Fujou Kirie (Passed on to Rie Tanaka).
Aside from that, Type-Moon has actually managed to get a rather consistent cast. It's not to the extreme of, say, Square-Enix, but I'm actually surprised it has stayed so consistent over the years (Without mentioning the anime that does not exist).
