I wonder if the following would work...
For both accounts and itunes libraries, use the same apple id. This should work on the same machine.
Unfortunately, that means the libraries between the two accounts would 'merge' oncd match does its thing and be the same under that one id in the cloud.
For purchases, one of the accounts would have to sign in with their ID in the apple store which would log them out of match. Logging out of match means you only have access to the files you have downloaded from the cloud or where already in the library. I think your purchased music would be fine and once downloaded to the library, when you log back into match would be picked up and placed in the iCloud library.
From what I can guess, you would have to be stuck with one shared library and this may not be what you want.
They didn't really make match to be a shared among accounts and instead locked it to the machine - probably because of the music licenses. With purchased/drm music and video thouugh, they can be shared across 5 appleid's. Very confusing. You have 10 devices on one id for match and auto/redownload of purcahses and you have 5 appleid's you can share content with.
I've got 4 machines, 5 apple id's, and one match account so far. Only two machines are using match so far (mine and a server), and just using homesharing for the others for now. Maybe when I'm bored I'll try to see if there is a way to activate match on all the other machines and also work with the other non-match Apple ID's. In a way, home sharing may be easier for the users of those ID's to pull from the master library matched from the server.