The new choson and Kallah go as well as their parents and often grandparents and siblings. They make a l'chaim, call their close friends and relatives and take a few pictures - hence the 'cemetery pictures'. Although at the Ohel there's a big 'tent' - corrugated metal building right outside the cemetery where the festivities take place.
I'll have to comment here.
Almost all new Chabad couples who find themselves in proximity to the ohel (and some from further away) will only announce their engagement after asking for a Brocho at the ohel.
Most go with there parents.
Some go with headboards and siblings too.
Many will say a small L'Chaim on their way out the door.
Calling close friends and taking pictures is definitely not part of the "custom" although that's usually what can be expected when a couple announces their engagement.
In short, in my experience and understanding it's not as much of a ceremony as ckmk47 makes it sound but it does take place.