It would be great if keyshot could keep the constrains made in an assambly in a cad program like Creo.
For example pivot points in hinges.
I think that is asking a bit much. CAD part to part constraints (not constrains) are not part of the geometry of the model so I don't see how they could possibly be imported. You can change part to part relationships easily in Keyshot, move parts or assemblies in x,y,z and rotate them just by picking the part or assembly. I rotate hinges in Keyshot easily using animation. Pick the part to rotate and then pick the hinge pin as the center of rotation. Works great.
If you have a mechanism created, you can bring that in now.
Check this out: http://keyshot.com/new-creo-and-proe-plugin-with-support-for-mechanisms/2013/ (http://keyshot.com/new-creo-and-proe-plugin-with-support-for-mechanisms/2013/)