Honestly this is quite an unusual setup, you have two recording devices and you’re trying to figure out if the same show is recorded by both the recording devices you don’t want MCEBuddy to convert it again.
No direct way I can think of beyond keep your output to .mpg or .mp4 or a common format so then skip reprocessing will check it.
They other way is like this, you can write a PreCustomCommand script that will check the destination file and look for a “match” in the other tasks destination folder (excluding the extension). If it find the file, return code -1 and have the PreCustomCommand fail it conversion before its starts. Don’t forget to set the PreCustomCommandExitCodeCheck=true