Yeah I think for cheap coaster brakes, standard auto wheel bearing grease should be good, a good quality one typically has a 500 F degree "drop point", the temp at which it liquifies and runs.

Something not cheap, like a Shimano Rollerbrake in an Internal Gear Hub, these have roller cams pushing out the brake shoes, and the hub is expensive, so I would try to determine what Shimano specifies; It could be wheel bearing grease, or could be a silicone grease.