Hello,
Third party controls are delivered as libraries. Most times you can use these libraries only if you write a wrapper library for such libraries.
I made some testing with the demo version of the Touchcontrols library from mirabyte and it worked quite well. Though it is much work to write a wrapper for this library which will support all members and properties.
So the answer for your question is: Yes, you can use 3rd party controls but you have to write a wrapper library for them. Be aware that there are 3rd party control libraries such the SenseSDK library from XDA-Developers which require .NET 3.5. I think it is not possible to support this library with B4PPC.
You can never use 3rd party controls in the designer. Not on desktop and not on the device.