Yes, there are perks.
But in the process of keeping cruise fares as low as possible for the public, those perks have been radically reduced over the past decade.
High ranking officers can still get great deals/free cruises for family on most lines.
For most everyone else, the system works much like the Guarantee fares offered to the public.
Several lines offer leftover cabin inventory at a discount to crewmembers just a few weeks before the cruise begins. It is usually too late to get a good deal on airfare.
The cabins offered are usually only insides and other lower categories.
If public demand for the cruise increases close to the sailing date, the crewmember's friends/family who purchased the discounted cruises can be cancelled.