Docker CE Overlay2
RHEL's kernel 3.10.0-693 do support overlay2 and Docker CE can use them just as well as Docker EE as the moby component of Docker EE and Docker CE are essentially the same.
The lack of support for CE here mostly just means the level of prioritization of features and bug fixes if you have problems when using overlay2 but don't own an EE license. When a CE user encounters problems/bugs with unsupported configurations, fixing it will be considered a low priority, so those issues are unlikely to ever be fixed unless it affects other EE users.