Don't worry about it! I doubt Delta Theta and Chi Omega Alpha are losing sleep worrying that their letters sound like NPC sororities.
*
edited to add*
AGDLynn, I see your point. However, there's another local sorority at the school we're talking about called Delta Theta, which is similar to DZ, which has chapters
everywhere in Ohio (we were founded there). I used to be mistaken for a member of that group every time I went to visit, but it doesn't bother me any. So I really think the name Kappa Gamma Delta is OK.