Yes, it means old holder. More commonly the term "No Line Fattie" is used to describe old NGC holders -- before they added a seam line between the part of the slab that has the label and the part that has the coin.
OH generally means the "fatty" NGC holders ( fairly tough grading), and OGH are the older Green PCGS holders, that tend to be graded more critically.
I don't know! I've been a member of the NGC forums for 10 years, and never once have I encountered the term "OH" for a fattie. It seems that terms like this are a recent invention spawned by the LT...............................no, not military officers.........................................just "Lazy Typists"! Chris