Hi Miha,
not sure about the reasoning, and afaik the oracle plugin is on the todo list of the checkmk devs but since it is probably one of, if not the most complicated (I didn’t say ‘hated’, but might as well have :D) to develop, its not an easy task.
Mk_oracle and remote custom queries - #13 by ricardof found a workaround to use the linux agent plugin to connect to another windows host and run custom sql queries, would that work for you?
Gerd