[jurialmunkey]

Inside the skin it's not possible, yes. It would be nice to have a info label like ListItem.UniqueID(foo).
I'll ask @ronie for a  possible implementation.

I dunno how you are checking against the local DB, but I do request all items in the initalization with a limited set of all items (costs me 1s, then it's cached). 
And for script calls I've added an option to use the DBID + DBType so the script will try to get the imdb id from the uniqueid table by itself.

Yeah it really is only from the skin side of things that it's an issue. I don't actually use local data for any lookups - I get online info first and then use that to search for a matching local item from jsonrpc (I check against imdb id first and then if no matches use title). I only merge dbid, artwork, filenamepath and streaminfo from local (everything else is online).

For the kodi db lookups I don't actually cache anything - i figure a local lookup with a list comprehension of matches is pretty quick and the slight performance cost is worth it to ensure I get the most recent info from local db. (it would be a pain if user had refreshed the library and so my cached dbid or file path didn't match anymore with their library)