In Canada, if you go to the manufacturer that made your car (i.e. Chevy/GM/Buick) they are OK with you stopping in for charging. Some other dealers like BMW are a little pickier on who can use them and they are generally located inside the dealer showroom so harder to access. Some are more receptive to you using their chargers if you call ahead and ask if it's ok to stop by and charge, and they don't charge you for using their charger. Again, this is Canada, in the US not sure what the policy/procedure is for them.
Although if they have DCFC now than that does suggest that chevy vehicles are good to charge there. Otherwise, why put in the infrastructure for a DCFC if it's going to sit there looking pretty and not be used.
Just my thoughts.