After about 7 months I can say without a doubt, this combo works. The arowana and the bichir both do not eat the snails. I recently added a clown knife, and he also does not eat the snails. In fact, the snails multiply so fast, I don't think it would have mattered. The only way I keep the snail population in check is with my weekly vacuuming. I typically suck up at least 10 to 20. These poor little guys then get thrown out into the grass or plants with the rest of the water-change waste.
I would say I have a current MTS population around 300 to 500 (tiny ones included), so if anybody lives in the houston area and would like to have some of these snails in their tank, I would be happy to provide free of charge. They definitely do a good job of tank maintenance, but beware of their rate of multiplication! I don't mind them, because they don't eat my plants, but some might. I think one of their biggest roles is not with algae, but with breaking down fish poop into smaller particles which are then more readily accessible to bacteria.