I did UVs using ZbUV Master on a cloned object and re-imported it into maya and checked if it was ok and all, and it was fine.
But when i paste those UVs in highly detailed model (on the lowest subd ofcourse) each face is separate and by this the UV count has tripled now.
Anybody with any solutions? 
I can’t be positive, but you might need to combine UVs in maya. Sometimes I’ve seen models come into maya with seemingly seemless UVs but if you click and move on you see that all connecting points are separated. If you select all UVs in your editor in maya then just do Polygons>Merge UVs this might take care of it. Again, I’m not entirely sure this is the problem you are having, but maybe give it a try and see if that helps.
I don’t know how one does it in Maya, but in 3ds Max I have to select all vertices and then click the Weld Selected SubObject button in the Unwrap UVW modifier. This welds all vertices with ones that overlap. Then it’s a matter of selecting each UV island one by one to make sure everything went smoothly. I run into the same problem with 3D Coat. For some reason the Unwrap UVW modifier in 3ds Max automatically breaks up my UV islands if the angle is above a certain threshold and I have to do the same method of welding to fix it.
I’m not sure my comment will help you, but from the sounds of it this is the problem you are having. I read another comment the other day by someone having trouble with ZBrush generated UV’s + normal maps when rendered in other apps. He felt unwelded UV’s were the problem because welding in another program would fix it. So if you know how to easily weld overlapping vertices (and only overlapping ones) in Maya, that should solve you problem. That is provided I understood it correctly of course lol.
Edit: Here is the link to the thread I mentioned.