yeah, it'll be fine to tighten the standoffs all the way. they are supporting the weight of not only ur mobo, but also ur GPU, RAM, CPU cooler, and cables tugging on it. you want them tightly into the mobo tray.
there are 2 reasons u want them tight
1) to support all the weight of the components supported by them.
2) so that should u ever try to remove the mobo, they do not unscrew instead of the screws that go into them (you don't want them stuck to ur mobo)