I reluctantly say that yes...you can cook a pork shoulder in a crock pot. As you stated, it won't turn out the same as a nice low and slo BBq in a smoker. But all of us don't always have the equipment or time to do things on a smoker. So I enthusiastically say yes...go ahead!
You can choose to get as involved as you like while cooking it or leave the shoulder be to the heat of the crockpot alone. At minimum, you can throw it in the crockpot with a little bit of liquid (1-2 cups) and let it go.
You can also choose to give it a sear to develop flavors that it may be missing. Since you won't be developing these flavors with any other method of cooking a pork shoulder, you may find it will help.
There are plenty of recipes out there for crockpot pork shoulder and any of them should do just fine. If you like you can follow one of the recipes or just add some spices as you feel are needed (ex) vinegar, Worcestershire, brown sugar, salt, spices and tomato paste) .
You can also go an entirely different route. A Mexican style pork shoulder turns out nice too. I line the bottom (and overhang the sides) with a couple of banana leaves. Then I throw in a good number of tomatillos, various peppers, white onions, garlic, cilantro and that's all I can remember right now. Fold the banana leaves over to cover the top of the pork shoulder and let it go. The banana leaves and each of the other ingredients really give a nice flavor to the pork.
Anyway you cut it...you'll be fine>>>>