You know what companies have not been disconfirmed so far: Sega, Square, and Microsoft (I think SNK is extremely unlikely). I know fan theory is that there is only one fighter per companies copyright. But just like Color Theory I've never truly bought that. Verge and Sabi may know that they aren't the companies and have never felt the need to say it. Or maybe they just never felt the need to ask. However, it is possible that their are no disconfirmations because they cannot be disconfirmed yet.
The characters in the pass aren't representing the company that owns the rights to them; they are representing their series. Joker, DQ, and Banjo are all about their series not their parent company. Terry, you can make a case for. With all the cameos and songs he does feel more like a celebration of SNK as a whole.
I can't know what the thought process was behind the DLC selection, but I just find it somewhat unlikely that Sakurai/Nintendo would cut out all the game worlds just because the rights were held by the same companies.
If I was forced to make a guess I would say Capcom and the other "new" companies are more likely, but I am pretty convinced of a large chance that fan theory is wrong and the character is from a company already in the pass.