Can I use my Cambodian entry visa for my muay Thai visa application and what issues might I face re-entering Thailand with a dtv visa?

AVOID POIPET BORDER CROSSING when returning to Thailand.

Yep that's totally what you do when you get to Cambodia, when you apply on the eVisa system you upload your visa/entry stamp to cambodia to show you're IN that country and can legally apply thru the system at that consulate. You use the hotel where you're staying as the "current address" and upload that confirmation too

Depending on your choice of land borders you may or may NOT have issues getting in. The Aranyaprathet/Poipet land border is especially bad. They could let you in, OR they could tell you to go to Siem Reap or Phnom Penh and fly back to thailand