Well, there is the whole fact that 'luz is just doing what he's paid to. I'm pretty sure we can rationalize that way. Bein' the sort who'd also 'just do what we're paid to.' That is, if we got paid to do things.
Sure, he did kinda get the drop on us, and drug us, but he hasn't really done anything else afterwards. Plus, he's been a pretty okay guy aside from the aforementioned bits. I'd think Kisume would be all '..Huh. Aside from the things he did a while back, he ain't so bad.'
Plus, him going free doesn't necessarily mean free in Gensokyo. He could easily get punted back to Kosa, we've got Yukari batting on our team for the time after all.