Hmm. How do I answer this without creating a whole lot more questions?
first, the easy questions: yes, maulbernauts are a subspecies of ulbernauts. Mercenaries and Thugs should be considered sentient beings of indeterminate race (because their faces are partially obscured.)
Semi-intelligent is a little tougher to quantify, but let me try. Creatures defined as "semi-intelligent" means they are capable of organizing societally, in some cases using tools and communicating in simple language, but are still mostly driven by instinct. (for example, a gobble might be able to talk to you, but will still attempt to eat you if it gets hungry. Not because it's evil, necessarily, but because that's its nature.) They are somewhere between animal and sentient. Semi-intelligent creatures don't go to the death realm: they only meet the true death. (Why they respawn in the same places is an OOC matter so don't bother to bring it up.) How should they be treated? There are a few tracts in the Octarchal Decree that can help you decide how they should be treated, legally.
Does that help?