Milcery can be bred naturally, so I don't think there's a connection. Milcery and Alcremie also apparently like being eaten and can regenerate their cells. This actually has some disturbing implications.
The real question is where the hell wild Tauros come from.
Tauros is an all-male species, the only way to breed them in captivity is to pair them with a ditto.
Some people have speculated that Tauros and Miltank are two radically dimorphic forms of the same species similar to the Nidoran family, based on how they're both bovine and exclusively male and female respectively, but a miltank will only ever produce militanks, even if bred with Tauros.