I'd say it's probably safer to go with a certain amount of ambiguity, since that's how the subject is treated in the games. I think Razlo in Shady Sands says that he doesn't understand how the Emperor Scorpion could grow so big as a result of radiation alone, whereas one or other of the FEV experiment disks mentions various different animals experimented on that could be references to critters that turn up in the game. Some of the escaped mammals could have ended up as the Molerats and other types of funky rat, whilst I had a crazy thought that maybe the tapeworms that are mentioned became the Floaters. I dunno, just my thoughts.
(Edit: discussion over. Point meaningless.)
(Edit: discussion over. Point meaningless.)