Glider time is total time and can be counted towards issuance of a CPL and an ATP in accordance with Part 61.
So if a regional airline requires 1500TT and an ATP then it’s acceptable time.

The 250hr requirement is if you change category.
So let’s say you’re rotor wing and you hold a helo ATP you need at least 250hrs fixed wing for the issuance of a fixed wing ATP.
Conversely if you hold a fixed wing ATP and you want to cross over to rotor ATP you need at least 250 hrs helo time.

Since there is no such thing as a Glider ATP it’s kind of a mute point.