Minecraft version: 1.20.1
Forge version: 47.1.106 (NeoForge)
Mod version: 1.20.1-1.2.1 (latest available)
GTCEu version: 1.3.1 (latest available)

Crafting Station is placed next to a Greg crate. When interacting with the station, no crate inventory appears:

I'm not familiar with current GT, but I'd speculate this is a problem on their side. Crafting Station doesn't do anything special, it just checks for a container with an itemhandler capability, and if it finds one it uses it.

Are there any special features to the crates? Can they be locked or anything like that?

Shouldn't be many special features - they can be taped to prevent item spillage is the main one. It looks like they're implemented as machines with bidirectional I/O, which might be causing problems? But IIRC things like smelters were accessible, so I wouldn't think that would cause issues.