If the airline check-in counter asks for a return ticket, you can show them your DTV visa. No need to buy a return ticket. I passed Thai immigration today with a DTV visa, and the officer didn’t ask anything for that.
Hi, I also applied on 22 April in Cambodia and am still waiting for the result. I think you might need to wait one more week. I've seen in other DTV groups, many applicants are currently stuck in 'pending approval' status.