i made a VIPER rat-manimal draysha enforcer...
Being as VIPER is buying Moreau's services to make Manimals for them, and ARGENT are hunting said Manimals, I'd say there would be some tension between them.
On Monster Island, probably. It's not clear whether Moreau is making manimals for VIPER, though. The Monster Island source book just says he gives them the "fruits of his research." The situation may not affect dealings between the two agencies elsewhere.
In any case, VIPER and ARGENT aren't allied strictly speaking. They just have a mutually-profitable association.
VIPER's interest in Moreau's manimal research doesn't extend that far. They were more interested in Draysha which is found in abundance in Moreau's lab. In fact, on more than one occasion it's made clear that VIPER has no interest in the manimal's except as guinea pigs for said experiments.