I asked one of the developers and got this response:
Actually OMQ has no pre-defined keep alive mechanism. OMQ is always accept the requests from clients passively, it cannot check the connectivity of client automatically.
OMQ can provide information about the status of the queue that the client attaches. If you can accept the hypothesis that client is connected if the its primary queue is attached, then one possible solution for your request may be: create an application which registers to receive availability (attached/detached) messages of the target queue from local Avail Server process. If the queue is available/attached, it means the corresponding client is connected. And if the queue is unavailable/detached, it means the corresponding client is disconnected.
Oracle Tuxedo Chief Architect