I do not usually run ubuntu anywhere so the gitian patches are not tested, I've only built with qmake. However they are directly carried over from ltc patches, so I'm assuming that if ltc will build correctly we will build correctly. I understand the need for gitian to do things like release signing, but so far I've not been concerned with release building. I figured that I'd leave that to you so long as you wish to continue being "point man" for the project. When I have some time I'll look into setting up gitian machines so that I can test this build flow in the future.
You don't need Ubuntu itself, gitian runs Ububtu in virtual machine. Gitian is usefull not only for signing but also to produce statically linked builds for Windows, it is possible to do it in some other way but gitian works just fine for that. I'm worring not about patches from ltc but about usage of C++11 things like system_clock that may be not available in earlier gcc version that comes with 12.04.