Yes, afaik, there is a problem with Carrara's obj export. I use Carrara 7.2pro and have the same thing happen a lot with complex "poser" content, not sure why yet, but it does. Without going into detail, there seems to be an issue with sub mesh /group referencing in the obj file. BTW if you use solely "in-carrara" primitives, it doesn't seem to happen ?? (very limited testing tho..)
As to multiple duplicate shaders, Carrara 7.2pro, not sure about C7 std or previous versions, has a feature under Edit - Remove unused masters - consolidate shaders.. which will assist in reducing the amount of shader duplication. Unfortunately due to the current limitation (imho) on obj out of C, its a bit of an issue..
If you need to get the model into Octane and its poser based, try Daz Studio, I use DS3 advanced, not sure if the std free version has obj exp, but certainly apart from quite material complex models it does a good job in faithfully referencing the materials in the mtl file and collating the maps etc for obj..
nfortunately as to my knowledge there is no consolidate material/shader feature in DS..
Hope this helps.
TF