There is a simple scale for water and dirt ingress, e.g. IP65 for protection from water jets and fine dust:
There are labs that test equipment and verify the claimed ratings. It should be simple for the bike or motor manufacturers to upgrade their seals by one IP step. Most suppliers provide a significant range of IP coverage in their catalogs. The price difference is probably small.
The only issue is that any maintenance on the motors has to respect the seals - understand how to disassemble and reassemble without compromising the join.