Well we've talked about this quite alot, and I've come down to a few theories. Firstly, the chee wouldnt have survived the blast any better than the auxiliaries. They can survive low blasts but a direct shot from the pool ship, nope.
And jake didnt know any of the auxiliaries that well, he didn't know which of them he could actually trust to ask to go on a suicide mission. Cause had he asked the wrong person, they would have freaked out and told the group and they all might have left. And if had second thoughts mid-mission and tried to get out, Tom would have found out Jake was trying to double cross him and the whole plan would have failed. Rachel was the only one he could trust to sit quietly through the whole thing, knowing she was about to die, and then to do what was necessary when the time came.