Ekeobinett,
Yes, I'm using diplexers on our ACE 27.1 with our Dish satellite. ( Holland STVC Satellite Diplexer
https://www.amazon.com/dp/B00BNXW21I..._kOxYxbW29MFRV ). One dilpexer is used to combine park cable and satellite dish signals to the single coax connector outside the RV. The second diplexer is connected inside the RV cabinet where the over the air antenna power injector is located. The exterior coax cable connects to the interior diplexer input. My Dish receiver is then connected to the satellite receiver port and the second port is connected to the CATV port of the original OTA power injector. Works well.
Beauty is no AB switch. Also, since the Dish receiver is HDMI and the TV coax connection carries the OTA or CATV signal, you can select between then by using Source on your TV. You can also view OTA/CATV and satellite simultaneously on different televisions.
Note that you only need the outside diplexer if you are using SAT and CATV. SAT and OTA combination don't require outside diplexer.
The install of the interior diplexer was a bit awkward because of the location inside an upper cabinet end wall. Take your time and have some short RG 6 coax sections available.
Good luck.