The Wii compatibility is different since the Wii peripherals have gone through a few changes (wired-wireless, etc). As it stands now, the RB1/RB2 drums are compatible only with GH5 on the Guitar Hero side.
Now for the real question of whether homebrew can overcome this shortcoming: so far, nothing has been developed. The main issue is that the games themselves do not initialize the USB slots or whatever other connections are needed and do not know how to read/mount the non-GH instruments. It would take either a modified game image or perhaps a very lengthy Gecko code to make the Wii auto-map a USB instrument into a non-USB game.
That being said, if you think you can wrangle the technical details of it, go for it and let us know.