I dont think it is a big issue, I've done it in several different casinos and there is no single issue when it comes to KYC although I use VPN most of the time. As long as we use VPN is not to bypass country restriction and as long as the casino is allowing us to use VPN to bypass providers restriction, we are good to go.
If the casino allows VPN and if you don't use VPN to bypass their restriction on your original location /country, you will not have problems with them.
Yes, bypassing the provider's restrictions is fine - I also try to use a VPN every now and then but not too often - it's just to get through the game.
Using VPN to bypass geolocation restrictions that are written clearly in a casino's ToS definitely results in big issues on your account and fund inside that account later. It's a risky practice and if you are not a cheater, I believe that you see this practice does not worth trying. Money is valuable, hard to earn so taking risk while you clearly know about bad consequence, is not wisely.
This is best avoided especially since it's not recommended in the Tos, in fact I avoid using a VPN at all costs unless bypassing provider restrictions.
Although some say the casino is VPN-friendly even I'm not brave enough to do so, fearing future problems.