No, generally encoding is done in software. It's just because VP9 is a much more complex format with many more different coding possibilities to search. It also hasn't been around as long as x264 to be hyper-optimized.

There are probably some issues with missing SIMD, but no further hardware support would be helpful.

It's purely an implementation issue - you don't get software as good as x264 just by paying for it.

Comparing x264 to hardware-accelerated encoders (QuickSync, NVENC, VCE), the speed/quality/bitrate tradeoff is massively in favour of the cpu-only x264. So i think hardware encoding could help VP9, but it's not a magic bullet (unless your CPU is busy with other work simultaneously).