Yes. The Cactus V5 transmitter has a pass-through hot shoe, so you can mount an on-camera flash directly on top of the V5 while the V5 triggers your off-camera flash.

A key limitation is that the V5 pass-through does not provide TTL, so both the on-camera and off-camera flashes need to be set and balanced manually.

Another option is to use optical slave triggering for the off-camera flash: fire the on-camera flash normally, and have the off-camera flash trigger when it sees that burst. Some flashes have optical slave mode built in, or you can add a slave trigger.

So the two practical setups are:

• mount the on-camera flash on the V5 pass-through and use the V5 to trigger the remote flash, or
• use the on-camera flash as the trigger source and fire the off-camera flash via optical slave.

For wedding work, manual flash settings are usually the tradeoff with this kind of setup.