In my humble opinion all of this is quite far fetched. Randy's appearance at the water pumping station and the attack on CJs may be connected; and yet both locations are quite far away from each other. Therefore a link is not really obvious and very arguable. Also we don't know for sure that this bearded zombie before the latest attack on The Colony is Randy; we only assume him to be that specific zombie, because he together with Ink are the only really individual zombies; althought the
Little Ones in LA are numbered, they are not half as individualized as Ink, Randy and the bearded zombie are.
Now, about Randy VS Ink instead Randy PLUS Ink ... I have doubts.
Michael does not say what has happened at the Water Pumping Station; we only guess - and that a lot, which makes anything possible. As for the attempt to kidnap Tanya things are equally uncertain - did Randy try to kidnap her in order to find a cure (then: how would he know about Tanya's skills as a doctor?) or in order to bring her to Ink for even more experiments? And finally The Colony: Why didn't Randy and the 'good zombies' interfere with the actions of the 'evil zombies', if they 'are'/'were' good zombies after all?
Again: Anything might be possible, but I have a lot of trouble considering Randy a "zeeh good guy" ...
All the best!
Liam