Marrowood wasn't always dangerous. A lot of the time it was fairly quiet to the point of boredom. But when it wasn't, it was nightmarish. And it was a lot to get used to and deal with. If Stiles was already prepared to deal with some of the horrors that crawled out of the woods at night, then he'd likely be helpful within the station and around it.
"Well then, we'll add you to the roster, you'll need to do a patrol twice a week, and you'll need to meet Rick and Shepard too." Rick mostly, so that he knew that eventually, Stiles might have some useful information, and to watch out for the kid too.
"A little research and fact checking, you know your book to what we have in the library here, that could be helpful for quiet time." If Stiles could have a productive time of research and figuring out the creatures here with his book while they were waiting for the next horrible thing to happen, then Emma figured that counted as smart waiting.
Emma just shrugged at the thanks, "Don't worry about it. Just don't get dead and we'll call it even."