Beyond being a suitable place to mount it,For a GMRS or 2m/70cm ham antenna it shouldn't be a problem. I run both on a roof rack without issue. I wouldn't run a CB antenna on the rack though and that appears to be what that antenna mount is for. You can get coax with a NMO end that has a 3/8" center so that it will fit the CB antenna mount hole and the mount looks to be just wide enough for an NMO antenna base though it would be nice if they provided some measurements on the product to know for sure.
Does the rack feature as a real benefit for ground plane, and were I to mount there should I consider an antenna that requires ground plane or not ? Thanks !