OK, I figure I'll weigh in. First, about the possibility of viable offspring, it's unknown. As Vanyard said, there's no evidence it's been tried. I did a bit of poking around, and the info on chormosomes on all Tupinambis is contradictory, so it's possible the babies would be sterile, inviable, or fine. Basically, there's no clues as to the results.
Now, many here know I'm quite supportive of hybrids, and find most objections to them shallow and baseless. That said, I'm not keen on 'undirected' hybridization. If you were trying to get offspring with a particular set of traits (say, a tegu with the size and docility of an Argentine with Gold tegu colors), that'd be one thing, but just because you don't want to buy a third animal is, well, lazy. Hybrids can be great animals, and can even be healthier than normals, but things *can* go wrong, so it's important to actually think about whether the benefits of the mating (producing a stronger or more desirable breed) would outweigh the potential problems if something *does* go wrong. Those problems are very rare, but they can happen. This shouldn't dissuade hybridization (the opposite outcome, animals with 'hybrid vigor', is much more common), but it should make you stop and think about why exactly you want to mate the animals you do.
Henry