Acid loops, Rex loops, Rewire,VST all proprietary yet all shared by multiple DAWS. The deals behind the scenes are probably not the same. I'm no software writer but I think an audio engine is a different animal and isn't subject to strict stipulations like some other add-ons are. At least, there are more commonalities in development than differences depending on the platform. Many DAWs almost undoubtedly share very similar architectures because of the nature of the design.
When it comes to sims there seems to be a loophole that allows for a computer generated copy to be constructed because it really isn't making the equipment in any way similar or infringing on the original design and it is usually named something similar so you know what it is supposed to sound like but they can't name it that.
Cakewalk has partnered with Softube and more recently with a few others. The bloatware you sometimes get with a new DAW , like a cut down version of Guitar Rig is likely a kickback to Roland but I could be wrong.
I see Cakewalk doing both their own development on new ideas and partnering when it might be advantageous to them and the customer. I personally have no problem with those deals because it usually adds up to a better experience overall.