Wow.. HSL is really weird then.. Flying pilot normally made all ATC traffic calls. Non flying pilot just backs him up in case he missed a call..
No we usually (individual AHC preference) have the flying pilot do the talking with the only exception being in a CAS role (reading back info etc) and FAC(A) (front seat talks to CAS agencies etc, back seat (guy flying) talks inter-section.
The HMLA as a community does not have a reputation for radio diarhea of the mouth though.
Seriously though, it's almost difficult to be a decent copilot when you first come out of the RAG since your comms suck, your checklists suck (very slow), and you still have no idea of what's going on. Aside from that though, typically the left seater only talks when the copilot is busy on the other radio (getting atis, talking to base, etc.) or if you're doing drops. In that case, the person flying talks to the drop master and the guy on the ground at the DZ (unless AC wishes otherwise).