Flint,
Not only have we done it, we use it on Citrix XenApp.
GE supports us, even on our own images.
We run our own images for Centricity, a customized Centricity Web (we SSL-enabled it and turned off integrated authentication so our docs can use it without having to log into the PCs under a Windows session), our own images for GE Viewpoint, and Intel NIC cards in our forthcoming Imagecast RIS servers (we told GE that we wanted Intel cards because Broadcom cards have way too many issues, and they agreed after we gave them the HP ticket # I opened up).
The only thing we don't customize are our GE Imagecast PACS servers and our hardware configs for them. Everything we do is by the book with GE on those, down to the switches.
Considering I had GE engineers on the phone debugging issues with Viewpoint on our image and our workstations (Dell Optiplex 760) with our team, I think that the same courtesy extends to Centricity. I got approval to SSL-enable Centricity Web from them.
I think they're a great company when they send out the good engineers, like every other vendor.
At this point, if GE reads this post, they know EXACTLY who I am

.