I don't think it's tacky at all. I think it's very nice to want to thank people who have been helpful, and I don't go to parties expecting a full-on open bar.
I do think it would be important to let them know that they are either welcome to bring alcoholic beverages, or that you DON'T want alcohol...whichever is the case.
A middle ground would be to provide some alcohol, like beer and/or wine, but not hard liquor. A LOT depends on how many people you are inviting, what your budget is, etc. Again, let people know what to expect.