An interesting use case. I don't know if that would work or not. The typical expectation is that the interface is either L2 or L3.
But if you had the similar connection on the SRX to the second EX switch and maintained the same tag it might work. You would need to setup the connection and test end to end.
edit:
And on the SRX you would need to be sure to add the new subinterfaces to the desired zone and make sure there are security policies to permit the desired traffic.