It probably would get mixed, but presumably there is a limit to the amount of taint a certain amount of saidin can contain. If there was no limit, the DO would surely have put so much taint on saidin that you could not even feel saidin. So presumably, if a smaller quantity such as EotW were tainted, once it got mixed back into saidin, it would be diluted to near insignificance.

Though if this was the use the ancient AS intended EotW for, it would mean that they probably expected saidin to be cleansed. Either that, or its not possible to seal the DO with a power thats tainted with his influence, making the cleansing absolutely vital to victory.

As for whether or not the taint would ever have been used up by male channelers, its possible. Given the efforts in all societies to kill males, and also the fact that they all died quickly anyway, its possible that the amount of taint that was "used up" since the sealing was only something like 10% or somesuch. The amount of saidin channeling has been very limited afterall.