Non-legal advice:

http://www.motifator.com/index.php/forum/viewthread/472185/

More direct (2nd hand source is supposedly Yamaha):

http://www.synthzone.com/forum/ubbthreads.php/topics/252218/1

Not exactly legal advice but defines what's fair use and what's not. A ZIP file of commercial sound fonts (including the free ones, btw - as they should be distributed by the source, not individuals) you intend to share with/to/from someone is not fair use. Charging $900 per LP of you playing clusters after turning on the keyboard using performance "CFX + FM EP" is fair use. Turning on and running through all thousands of ARPs using some performance from the Blue Man Group ... as your second album and charging $0.50 per digital download is fair use.

Not getting into the other copyright entanglements which are outside the scope of what you asked. Just sticking to stock/purchased/free performances/libraries and stock/purchased/free ARPs that come along with all that.

Without a sampler - Montage digs a smaller possible hole than previous gens with respect to possible infringements. Although now this is pushed into software.

In other words - you can get into deeper waters by using your own "produced" content (sampling other artists and adding echo - or just calling the "cut" some form of artistry) rather than ones that come with the keyboard or lob on to the keyboard (purchase, download).

Standard disclaimer about not being a lawyer or anything close applies. If not satisfied, feel there is some risk from what you're doing, and you have the the funds - do consult with a lawyer to get a more trained/precise/sound answer.