I tried apply the firesight license (FS-VMW-2-SW-K9) on version 6, and the follow message appers:
"FireSIGHT licenses are no longer required for Firepower Management Centers Version 6.0 or later"
It is no longer necessary license since version 6?
That's news to me.
The current Ordering Guide (dated November 2015) indicates that the license is required.
I haven't built a new one using Version 6 though - only upgrades. Those certainly use the license