Yes, they are a fully owned subsidiary company of Bangkok Airways. Obviously set up so PG could operate domestic flights on the high volume PNH-REP tourist route (Angkor Wat) inside Cambodia.
They have no acft of their own, all done by PG ATR72's. These ATR's have "Siem Reap Air" on the fuselage aft of the wing (see pic).
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Photo © Alastair Bor
I did see a very colourful model of an ATR72 in a Siem Reap Airways c/s in a travel agents in Phnom Penh, but according to the staff the acft doesn't exist.