LinqKit is not magic, it can't see inside EntityMatches()
or otherLib.IsEntityMatch()
, so there is no way it can help you translated those into SQL.
What LinqKit can do is to create a complicated condition out of simple parts. But each simple part has to be translatable into SQl by itself and I don't see a way how to do that in your case, especially since you're using some external library.