So I tested my Vive on a laptop I have with a GTX 1060, and I get the same issue, like with you. One GPU, though it still says the monitor and the HMD are connected to different GPU’s.
I’ve tried, on both my desktop and my laptop, to set StewmVR’s and the game’s GPU to whatever one the monitor is plugged into, but to no avail.
I also wanted to mention something else odd: VorpX desktop viewer works on my Vive, but it has never worked for my Rift.