Negate: Time Trapper can use Outwit. When he does, he can use it normally or choose to counter the same power or team ability possessed by all opposing characters to which Time Trapper has a clear line of fire that are 6 or fewer squares away.

Can Time Trapper use Negate to counter a team ability that blocks line of fire, like the Batman Ally TA?
Yes... if he can draw line of fire. Specifically, say he can draw line of fire to Batman and he chooses to use Negate to counter Batman's TA. That's fine. However, Robin, who also has the Batman Ally TA, is within range but Time Trapper can't draw line of fire to Robin; Robin's TA is not countered.

If Time Trapper counters a TA, can opposing wild cards still choose to use that TA with their wild card TA?
Only until the end of the current action (which would be the free action Time Trapper used to activate Negate). Once the "source" of a TA is gone, countered, or otherwise unavailble for any reason, the wild cards can't use that TA anymore once the current action resolves.