Speaking from the position of an end user and having only encountered a handful at any given time...
Not all of them are hostile for starters (usually you can at least depend on the Friori and Leorians to be your friends,) but the main thing to look out for is disease resistance for your own guys (which can be buffed by providing ample amounts of magebane or venombane drinks,) and anything with large size noted in its description. If nothing else, big boys need edged weaponry to deal with, forcing you to field more weapon-diverse forces (as bigger enemies are simply too beefy for mace or hammerdwarves to bludgeon to death efficiently.)
They're otherwise much more forgiving, at least of the ones I've fought or had serving in my militia as sellswords, lacking crap like metal-grade tissues barring specific areas of the body on some races that explicitly artificial augmentations. Course some of them have multiple arms, don't feel pain, inflict pretty serious status effects or have hard-hitting projectile attacks if memory serves, among other things. They also have a very wide array of weaponry that might make them more or less dangerous; having had no use for thier inferior quality weapons I can't speak of performance.
Overall, standard tactics will usually still carry the day for you, and if any show up wanting to soldier it couldn't hurt, particularly the casters who will be just as dangerous to your enemies as they are your own people.