No it's not. Kremlings have been implemented in a context where every franchise is getting enemy rep. At the time of development DK only had two viable options for enemies and both got implemented. It's unlikely that Sakurai looked at the Kremlings and pondered how to implement them in the game. Instead what probably happened is that he knew he had to add DK enemies and he realised that Kremlings are one of two options he had. The fact he decided to go with the Tikis as well suggests he was probably just going for the general enemybase rather than making a point of just using the Kremlings as if to say that they are the true DK enemies.
There's no equivalent context for K. Rool. It's not like there's a rule where every franchise has to have it's most recurring villain playable (although that probably would be a good rule). He could be playable but I don't think this counts as a legitimate indicator.
Except the bolded isn't true at all, from what we've seen. Nothing from Star Fox, nothing from F-Zero, nothing from Wario, Fire Emblem, multiple retro and new series, and so on. Sure, "we haven't seen everything yet," but that excuse dies in a week, and not every series will have content hidden away everywhere we don't currently see it. Someone's getting the short end of the stick, and it's not Donkey Kong (at least in Smash Run), specifically its Rare era, even though "Kritters are irrelevant" is a ridiculously easy excuse to throw out as far as just using multiple Tiki variants and calling it a day, before adding in another dozen Uprising enemies.
Also, I don't understand why it's a Herculean task for people to consider, maybe, a "new" character didn't get in because they're "new," a reason Sakurai
has never, ever advocated and has outright contradicted multiple times, but because they're unique, a reason Sakurai
has gone out of his way to mention in the majority of interviews he does, they just didn't exist in 2005 or earlier for Brawl consideration.
