Hi:
If you imported and 3D scanned meshes, is normal to receive some warnings from Mudbox.
The scanned meshes normaly are totally made of triangles, and sometimes you can have areas with "poles", this is, more dan 5 or 6 edges coming to a single vertex, and other situations.
Someone are more problem than others. That is because Mudbox started like an 3D sculpting and painting soft for visuall industry, like films, videogames, and other areas, where the workflows hightlight the clean meshes for animation, texturing, and so.
If you are planning to use your scans in Mud to make some fixes by hand with the sculp tools or paint tools, and these scanned meshes are for 3D printing there is no problem with the warnings in Mud.
Normaly the 3D printers use triagulated meshes with no problem,(obviously you need to make some inspection to the model with an dedicated soft, like Autodesk Meshmixer, to next generate the STL or maintain it in OBJ if your 3D printer support that file format.)
I have worked several times with scanned meshes from clients that want to do some type of resculpt in their action figures.
In those cases, what I do, is, in the possible, run an retopo operation for the mesh, to generate a new one with all quads. In the most cases mud can deal with triagulated meshes and/or with some gltiches. If your scans have holes in the mesh, I recomend to use the commans Mesh>Patch, previously to run the retopo operation.
Sometimes could be some small glitched areas in the retopologized model, due the ugly geometry of some scanned meshes. In this case, I use a bit the sculpt tools to make fixes by hand.
If your mesh is so ugly, that the automatic retopo fails...well, I normaly start a new mesh, using the original scanned like reference. I lock the triangulated mesh, and start with an sphere,sculpt tools, and retopo, until I get the general forms the most similar to the original.
For the final touch I run an Mesh> Transfer Details operation, to transfer the fine details from the original to the new one.
If you create good UV coords for your new mesh, you can make an transfer paint layers operation to transfer the paint color textures to the new mesh...
This is...sinthetic. I hope would be helpfull. Perhaps in the future I'm going to upload an videotutorial to my youtube channell dedicated to the workflow in Mudbox with 3D scanned meshes for 3d printing.
Greetings:
Sergio Mengual
3D Artist-3D Generalist-3D Character Artist
https://www.artstation.com/artist/sergiomengual
https://www.facebook.com/Sergio3D2D/
https://www.youtube.com/user/sergiomengual