The configuration syntax is there to support multiple VLANs in a single static GRE tunnel yes. My 6.3.1.1 controller allow me seemingly to put lots of VLANs in it (hundreds). My understanding is that the VLAN IDs are retained within it.
I can't say I've implemented it on that scale though, so couldn't comment on performance. I've done a few with a couple of VLANs in GRE inside IPSEC (public traversal). I supose as long as the controller is a big one, and the network topology throughout could sustain the tunnel scale/potential, it sounds like a reasonable idea (unless the Aruba guys say different).
Personally, I'm not a big fan of these architectures, but in some cases, it's needed of course.