Looks interesting. Seems like it would be almost as easy as it would be with Maya to add some humanoid rig. But in my opinion this makes more sense if you have a character without any skeleton and without any weightpainting. Makehuman already provides a skeleton and the weightpainting works well. I would still recommend to keep it and just fix the rest-pose.
That said… I’m even no big friend of all those “GPL” blend files. While it’s probably ok to be a bit pragmatic in this case I don’t see a real benefit to move into a possible grey-zone. Both the UE4 Tool (if you get it from github) and the Auto-Rig pro (which is even available from github as well in an older version) contains blend files and are distributed under the GPL without an exception for the blend files (well the UE4 tool could be downloaded from LUIs site which does not contain any license info as well). I think non of those plugin creators would restrict the exports (I guess) but leave the users in an unclear state. Probably this differs from country to country. GPL is a great license for open-source software but an annoying license for any media in a closed source game. While exporting something from a GPL program does not cast the GPL to the export (the export is out of the scope of the GPL and exports from Blender are stated as your own) it even does not clean the GPL from imported media that is already under the GPL (e.g. images, blend files, …). For example if I create a cool character (or Rig), put it under the GPL and share it with the world (only) under this license it would be too less for somebody else to just import and export it with some (GPL or non GPL) program quickly to remove the GPL from it. That’s the reason why Makehuman added an export exception. If you export a mesh from an (unmodified) version of Makehuman it got the CCO exception (so you may use it even in closed source software). It’s similar with ManuelBastioniLab but you have to give credits as well (which is perfectly ok for what you get afterwards). It even protects the export between the users a bit. If you put all those body mass sliders into the same 0-1 position (by luck) as another user somewhere else in the world both may use it and nobody could say it’s his own. Only the modification (beyond those shape target sliders) that are made by you afterwards are your own. In short: That’s a further reason why I would prefer using the (CC0) Makehuman skeleton over (replacing it with) a skeleton that comes as GPL blend file somehow. The Makehuman skeleton fits perfect to the mesh got well working weightpainting. Only the rest pose differs a bit (which is not that big issue). And regarding the weightpainting of the twist bones it seems either of those tools leave you into a position where you have to do this your own (currently). This should change with 1.5 of ManuelBastioni lab.