I have been playing around with this for a while and have also just had some pretty good and simple results.
Originally I was running a 5.0 ESXi install and got an XFX 5450 and a VTX 7750 running with passthrough. I additionally had an Asus Xonar STX sound card which worked no problems. I ran this a while and managed to even play a few lower end games in eyefinity with the 7750.
I moved house and my setup/requirements have changed, I am now planning on placing this in my living room. As well as a few other linux VMs the plan is to have 3x VMs using passthrough.
1. XBMCbuntu (XFX 5450)
2. Windows 7 running Hyperspin (emulator frontend) & Steam (VTX 7750)
3. Windows 7 running Argus TV server (TBS 6281 DVB-S2 sattelite card)
I don't have the card for the 3rd yet but over the last couple of days have got the first 2 working.
The XBMCbuntu install couldn't be easier, GPU passed through from the initial setup and it boots straight into it using the 5450 HDMI output. I expect I may need to replace the 5450 with a 6450 in order to get HD audio.
For the 2nd windows install after one failed attempt it has just worked. Last year I had all the BSOD problems with atikmpag.sys and it looked to be the same on first attempt. Second attempt however was as smooth as could be:
1. Install W7 in VM and update fully - including .NET 4.0 framework
2. Install VMWare tools
3. Enable passthrough of devices
4. Install AMD 13.1 drivers
That was it, the display activated without even rebooting after the driver install.
This is all on ESXi 5.1.0 799733, other hardware specs are:
MSI Z77A-G45 motherboard
Intel i5 3550 CPU
16GB RAM