As far as being homozygous for red, he isn't. He was always bred to something similar to himself to throw the same color. If you bred him to a black tobiano mare, she could throw a red black or bay foal depending on what genes she throws and if she was dominant for black.
With the color, every time you breed two tobianos together, there is a chance for a homozygous baby, TT. If he has ancestors on his sire's side that are tobiano, I believe there is such a thing called the "Barlink Factor" that could mean he was still passed those genes. Don't quote me on that though, since I'm not sure.
If he could be a carrier of the OWLS gene, I would have him tested, that way you can be sure not to breed to a mare that is also a carrier, if that mare is tested. There is a chance that foal could be a lethal white, which would die within a week.
Alot of breeders won't even breed a horse that is a carrier of OWLS, hopeing that if people are more careful on what they breed, the OWLS gene will fade away.
Genetics for my tovero mare who is now sold was TtEeAa, she was a bay tovero and threw a solid chestnut filly with a little white throughout her coat, but I don't think its enough to reg. Her as a sabino. My mare had lots of roaning on her neck and on the edges of her pattern, and might be considered a sabino, since she threw it to her foal. IDK lol.