While I appreciate Sheriffs who do this...
When they step in and arrest the feds, vs just not helping them, then they're doing something. When the ATF comes to my gun club to arrest me for shooting an SBR, if I call 911 and the Sheriff comes out and puts the ATF in cuffs, then we're getting somewhere.
While I love the idea of local LE cuffing BATFE agents, given the I don't think it is likely without first overturning Supremacy Clause immunity, which I think is unlikely.
However, it doesn't take a Sheriff violating Supremacy Clause immunity to effectively nullify Federal law.
There are over 700,000 non-federal LE out there, and only 2,500 sworn BATFEIEIO types. Not a lot is going to get done if local/county/state LE doesn't play ball with the BATFE. Note that in states where marijuana has been decriminalized the feds have tended to drastically scale back enforcement, often not even bothering to target state licensed businesses. It would be child's play for the DEA to find people openly selling marijuana from storefronts in many states, but have not tended to prosecute those cases in part because of lack of local/county/state LE support.