As far as I know Shuffle is VPN friendly casino so We can assume that its safe to use that as long as they are in allowed region and don't have any intention to violate something on their casino.
VPN or not.
If you ask me to choose between VPN & Custom DNS. I choose or more prefer custom DNS, and avoiding problem in the future. We seeing so many case while most of the support said (It's fine use VPN, promotore/streamer suggested VPN) still we seeing some case about those and they brought VPN as the problem even telling them support said VPN is faid.
Better than avoiding some problem in the future.