Sí, Cameron lo aseguró en distintas entrevistas tras el estreno. De hecho, esas declaraciones también se citan en imdb:

Real oxygenated fluorocarbon fluid was used in the rat fluid breathing scene. Dr. Johannes Kylstra and Dr. Peter Bennett of Duke University pioneered this technique and consulted on the film, giving detailed instructions on how to prepare the fluid. The only reason for cutting to the actors' faces was to avoid showing the rats defecating from momentary panic as they began breathing the fluid.

Fluid breathing is a reality. Five rats were used for five different takes, all of whom survived and were given antibiotic shots by a vet. The rat that actually appeared in the film died of natural causes a few weeks before the film opened. According to James Cameron, the scene with the rat had to be edited out of the UK movie version because "the Royal Veterinarian felt that it was painful for the rat". James Cameron repeatedly assures that the rats used for this take didn't suffer any harm.