A lot of progress has been made recently in ARM virtualization (see its push into datacenter units). An ARM VM should run reasonably quick, and Ubuntu works fine on ARM.
Sure, but if we're deploying to x86 servers running Linux, then running Ubuntu on virtual ARM doesn't seem terribly wise[0] — it won't tickle the right bugs.
[0] For my money, running Ubuntu in general is a poor idea. It's not a great server OS, so it shouldn't be on the server — and if it's not on the server, it shouldn't be on the development systems either. Just run Debian everywhere.