Yes, we've run into 2 or 3 ZFS bugs that I can think of that were resolved in a timely fashion (released within a few weeks if I recall) by Canonical working with Debian and zfsonlinux maintainers (and subsequently fixed in both Ubuntu and Debian - and upstream zfsonlinux for ones that were not debian-packaging related). Of course your mileage may vary, and it depends on the severity of the issue. Being prepared to provide detailed reproduction and debug information, and testing proposed fixes, will greatly help - but that can be a serious time commitment on your side (for us, it's worth it). Hope that helps!