The nebula is full of gas the colli can use. Then again, all those transports for the colli was for a big preparation for the colli intended for a big sustained crippling of the ntf. We've never had missions with such transports for destroyers before. Who knows how often they need them let alone the colli. This is something that's rather big to speculate on, sort of like subspace drive recharge time.
Sensor range in the nebula wasn't that bad. Yeah you'll get an awacs in there of course, but even still, otherwise other ships in the nebular theater would have pulled out too. In fs2 we do get to escort a lane of transports into the nebula. For the most part, that was easier than doing the transports for the colli. Then again, the shivans really have some **** fighters, weapons, and fighter tactics. I only give respect to the shivans awesome big ships, all their bombers, and the mara, dragon, and astartoth (only problem with the astaroth is that it seems rather ineffective when in the wrong situation, it really seems the shivans have an interceptor for nothing). But bombers going after a transport convoy? That's a little over kill for the shivans and they always do it; not hard to take down big bullseyes.