Calypso is not owned by Neverdie, no.
Regarding the old Calypso mobs appearing on Rocktropia, there's a simple explanation for that. When FPC and MindArk split there was a dividing of assets, including mobs and item designs. The mobs and items that went to MindArk was put in a Shared Folder which all Planet Partners can use from. Kind of a Planet Partner Starter Kit, of sorts.
This is also one of the reasons for the Shinkiba. We wanted to make a version which was entirely our own (and more kick-ass.)
MindArk isn't necessarily behind the spawn size, no. Planet Partners can also script spawns, how many and where its placed. As for the mining fields, I don't have any insight to that. :/
Also, if we feel any other Planet Partners are somehow disrupting our Planet, make note that would be something we'd deal with internally, not on a community forum. We're taking it seriously though, and the feedback which you provide here will be made use of.