I used to be a moderator on the technical support forums for 3DConnexion for about a year. I even got a free SpaceExplorer for helping out.
Some of the information you are looking for may be in their forums. There is a developer section where you can post specific questions like this. The 3DConnexion engineering staff themselves are the moderators for that section of the 3DConnexion forum so you can get info directly from the very individuals who design the devices. They work closely with many software companies and may have information available from them that might be useful to you.
On the 3DConnexion website there is a toll free number to call their phone tech support. The people at that number won’t be able to help you directly with an SDK issue, but if you tell them up front that is what you need assistance with, they will put you in touch with someone who can get you in contact directly with a specific engineer who may have the information you need. It has been awhile since I did some work for them but if it is the same person, then the tech support people will likely get you in direct contact with Ken Denton, one of the vice-presidents there who coordinates all that. I think I still have his phone number somewhere but I’m not sure where at the moment. Anyway, it is easy enough to ask the phone support people to get you in touch with him if he is still the one in charge of that.
I recall they were investigating it back just before Z3 came out but I never heard anything more definite after that. In most cases they provide the SDK to software developers and 3rd parties to develop the support in their software for 3DConnexion’s hardware. A smaller percentage are done internally by their engineers in partnership with certain software developers like Autodesk.
Let me know if this helps as I would LOVE to be able to use my SpaceExplorer in ZBrush someday. It is such a huge timesaving device, I don’t know how I would manage in Max, Sketchup and Photoshop without it.