There are many who do that. Net hashrate above 4 MSol/s at average hashrate of single GPU about 50 Sol/s. So It's about 60-90 thoushand GPUs involved in BTG network.
What exactly do you interest in ?
Probably even more. There are a lot of NVidia 1060's that were put into mining in early 2017, being very power-efficient miners of Ethereum and Zcash. They can no longer profitably mine Ethereum or Zcash given most people's power rate, so they've moved into BTG.
Also, newer miners for Equihash(144,5) (aka Equihash-BTG aka Zhash) are supporting AMD, such as the latest lolMiner (https://bitcointalksearch.org/topic/lolminer-164-fastest-kaspa-miner-in-market-4724735) - supports mining on 560s and Vegas with only 3GB RAM. While the rates are low - below 50 Sol/s - they will give more miners and individual GPU owners the ability to mine again.