Comment 13 for bug 392510

That wiki page is a little old: https://wiki.ubuntu.com/DmraidSupport
Ubuntu must support it if its in the installer CD and in the main repos so I'm unsure if that is just outdated like most of the online documentation.

I have been using dmraid (and bios raid) for years and have had no issues so I consider it very stable and usable.

I'm not sure how dangerous your setup is. It may work for you but someone with a different style of BIOS RAID controller may get issues if it stores metadata in special places which will mess with mdadm. Or worse if mdadm accidentally overwrites metedata for the bios raid and you loose the entire array.