How to check if a floating license(xPlm CadConnector) is in use or not?

License Manager was my first thought too. Have you ask Aras about this one already?

This information is not in the License Manager most of the time. If it is the information there is not accurate. 
I have tested with users, had them login and use the CAD connector and the License Manager would show 2 out 5 are using the license, which is not true. Sometimes, when you refresh the page it would show no one is using it. The login dates are also incorrect 

I hoped anyone else would have know the answer to this question, but so far no other user showed up.

I recommend you either ask Aras Support, the Licensing team or just directly call the next Aras office in your area.

Of course Aras likes when people use the forum to find answers because it means less work for them :).  But sometimes you will not find an answer here. You pay good money for the connector and your question doesn´t sound unusual. So just ask them directly. Other users probably ask the same question before.