So when you're using it as an attenuator, you've obviously placed it in between the OT section of the combo, and the combo's speaker jack, yes? This is the only way for it to work as an attenuator so I'm guessing the answer is yes.
If you're not getting sound out of the Captor X with it connected to the speaker out of the OT of the HotRod Deluxe (and NO speaker leading back out to the combo's cone), two things:
1) have you tried the output signal on the front panel?
2) if using an audio-interface, have you moved your settings to be headphone-out only on the interface?
Quick litmus test - disconnect the TRS/XLR from the Captor X to your audio-interface, and just connect headphones directly into the front panel of the Captor X - make sure the speaker from the OT section of the amp is FULLY plugged into the socket of the Captor X - sometimes it's only a tip in and it messes with the signal; then plug headphone direct in front of Captor X, use low amp volume to start, and bring the headphone output signal up slowly while playing - it's gotta work!!
Peace