Yeah, the actual POH for the airplane suggests/commands that you add power to the rear first for the reason you thought: to verify that it is producing power.
An engine failure at gear retraction is probably the worst thing since the gear doors open up like big clam shells. We always waited till 500' before raising the gear as a preventative cause. Might have been a little conservative, but that's what the boss wanted.
Other than a few quirks, I really enjoyed the Skymaster. It perfomed well, went fast and was economical. We used them for whale surveys off the coast of FL and with the power pulled back to 100-110 kts indicated at 1000 feet the engines were burning a total of 12-13 gallons an hour.
I would assume that everything is the same on the PTS except for the VMC demo, but like I said, ask the FSDO about the centerline thrust rating, although according to 61.45(b) it looks like its still legit.