sure they probably don't deploy from TIE's, they probably have a shuttle of some sort. But in a galaxy spanning empire with resources enough to build two planet destroying guns? safe bet that they could train their spec ops personnel to fly star fighters and give them suits useful for flying and operating in space just in case the mission requires it.

Also a safe bet that not every star destroyer or planetary base would have a spec ops team and that they'd have a base of operations somewhere that they'd launch strikes from, tagging along on larger vessels when they have to, which no doubt the officers in charge of those ships would ***** about constantly because they're having to give up precious space that could be used to hold their own complement of star fighters to whatever is needed for these spec ops people.