No it has been fixed in 1.13.1.
Recreating the world in 1.13-pre1 fix the problem, mobs will spawn again, but everything build in the world in the snapshot 18w16a is gone. If I update my world from 18w16a to 1.13-pre1, only the chunks that I load in 18w16a will have this bug.
No it has been fixed in 1.13.1.