I'm not seeing this behavior here (iMac 5K with 10.10.4) with PS CC 2015/ACR 9.1.1.
What happens if you disable "Use Graphics Processor" in ACR preferences?
Can you post a sample image to Dropbox (or similar) that we can try to reproduce the behavior with?
I've had the exact same thing happen with my 2013 Mac Pro when using Camera Raw/Photoshop CC — I'm running Yosemite, and have been updating it as Apple has released new versions, so this happens with Mac OS X 10.10.4. Frequently, the Camera Raw toolbar and panel interfaces do not appear completely. Sometimes they don't appear at all unless I roll my mouse over the blank areas where the tools, tab icons and sliders should be visible. This only happens some of the time— not all of the time, but often enough to be exasperating. If I zoom in to the image, the interface appears. Not sure if if this is specific to CC 2015—I don't remember if it happened with 2014, or if this has been a problem since I first installed Yosemite.
I've experimented with the GPU preferences, turning them completely off, trying Basic, Normal, Advanced, Open CL on or off, etc. Nothing seems to fix it completely.
I had Googled in vain to see if anyone else has experienced this. I haven't been conscientious enough to do screen captures of this phenomenon on my Mac Pro (3.5 GHz 6-Core Intel Xeon E5, 64GB RAM, AMD FirePro D500 GPUs). Now that I've seen that someone else has had the same problem in Camera Raw, I'll try to document this weirdness the next time it occurs.
I did work on another similarly configured Mac Pro recently and got other bizarre graphics problems with CC 2014— not in Camera Raw but in the main Photoshop work environment. This was with the GPU enabled. I posted a zipped folder of screen captures to my Dropbox. You can download them here:
Dropbox - weird_Photoshop_GPU_bugs-Larry_Auerbach.zip
There is a new GPU preference in ACR 9.x, itself, which is different than the Basic, Normal, Advanced you mention in the PS preferences.
Screen captures are much easier for forums users to see if you just include them in the web version of the message using the camera icon next to the video icon on top of where you type in the text of the reply.
I had this Camera Raw glitch appear last night on my Mac Pro, not long after posting my above comment. I tried to reproduce this today, but wasn't able to. Not sure what the cause is—it's not the "Update to Current Process" button you'll see in these two screen captures. If this was happening predictably, I would turn off the Camera Raw "Use Graphics Processor" preference to see what happens.
As you can see, there are other parts of the interface that do not appear: the Toggle Full Screen Mode icon, the Select Zoom View icons, and the Swap before/After settings. Weird, eh?