I don't think they would object, I just think that it would be preferable for them to officially support standard play + VR play, since they won't really be able to force people to use VR.
If you watch the video I posted earlier in this thread it's very clear they're designing for VR. It's pretty clear they want VR to be more mainstream/popular and are interested in the design challenges of a VR game. They're selling a $1,000 VR kit. They're paying for VR game development by pre-paying Steam revenue while still allowing the games they're funding to appear on other platforms.
Valve doesn't operate like other companies, I'm sure they know they're going to sell way less copies of Half Life VR as a VR only game than if it had a normal and a VR mode. I doubt they care about that loss revenue. I wouldn't at all be surprised if they discount HLVR or give it away for free to Valve Index buyers. It seems like their current goal is to increase the number of owners of VR hardware (and subsequencly the number of people buying VR software, on Steam and other platforms).