Maybe it is this generation's Drowzee. A lot of the games have near-to-exact copies of other Pokemon. Examples being Rattata, the first generation Normal-type and then the similar Sentret, who is also a rodent and is a normal type and, like Rattata, has only a single evolution. We had Pidgey in the first generation and Tailow (still a bird despite connection not being as deep) in the third, Starly's eerily similar evolution line in generation four, and, apparently, Mamepato in the fourth generation. First gen was Magikarp, and then Feebas in the third, and you'd have to be as blind as a Zubat not to see the similarity between those two evolution lines.
Perhaps Munna is the Drowzee of this generation. Drowzee can learn Dream Eater after all, so if they're not related then perhaps it's just unimaginative spam, so to speak.
The only support I can find for this theory is that Munna does slightly resemble a "baby" Pokemon, due its height and obviously feminine features. Aside from that, the colors don't even vaguely match, so that's, in my opinion, the closest thing to evidence for the case.