Like I said in my post, at least some little person actors (is that still the preferred term or have they gone back to dwarf?), find these kind of roles offensive and don't like to do them. So this could be kind of a lose/lose scenario for the people making the movies. Cast little people in the roles and some people will say it's offensive stereotyping, but cast tall actors in the roles and some people will be upset because they say you're taking roles away from little people.
This a case where I could kind of see both sides of the argument, the oompa-loompas are not necessarily the most dignified roles, but at least it could still get little person actors some work.