I’m not aware of anything BridgePoint does to explicitly restrict Java threads. I suggest you follow the Developer’s getting started guide (https://github.com/xtuml/bridgepoint/blob/master/doc-bridgepoint/process/Developer%20Getting%20Started%20Guide.md) to build BridgePoint yourself.
Once you have it built you can use the you can run the Debug Launch Configuration “Eclipse Application > BP Application”. Then you can use the JDT debugger to set breakpoints, see the stack, watch variables, look at threads, etc…
Verifier is implemented in the org.xtuml.bp.debug.ui plug-in. I suggest you start by looking around in there.