Ron is a lot like David Warner (both Fo1 voices). While both of them have enjoyed a certain success on film or on stage, both of them also enjoy working as voice talent. That goes the same for many of the people who voiced on the Legacy of Kain series (excellent voice acting, even if it's made annoying in the first one). Charlie Adler, another Fo1 voice, is mainly featured in cartoons like Cow & Chicken.
Many actors do voice talent to buffer a bit of their spending account, or just for adding a bit of fun to a game. Michael J. Fox is doing a lot of work in animation and from what I hear, he's working voice talent for a game.
Bruce Campbell, the king of cheese, baby, does part of the voice narrative of Spider-Man 2, for many reasons. The love of the setting is one of them, but it could be that he's Sam Raimi's bitch.
Voice acting for games is a lesser known aspect of Hollywood talent pooling, right under cartoon voice acting, but it is often looked upon fondly because they and their kids like playing the games, too. It wouldn't be hard to imagine Ron Perlman as a Fallout fan. After all, he's worked in a number of odd roles, including City of Lost Children, Aliens 4, Hellboy, and a few others. He does like the genre of both setting and I believe gameplay of Fallout, though I haven't heard any concrete information to the effect of the latter.