if you make several small passes the dremel should work. it doesnt have enough power to make a slot cut in one pass, probably need 3.
also if you dont want to get a slot cutting bit, you could always use the standard plunge/cutting bit and set a jig up to run the dremel along the edge and not along the face of the material. Again with this make 2-3 passes, puts a lot less strain on the tool/bits.