Okay, I think I've found the easiest way to setup a room to make two specific dwarves meet and greet, be it for making friends, or for getting married.
It just managed to get 2 of my founders who had been lovers for 6 years, to get married within a dwarfweek after setting up the room.
It's easy. Get two dwarves into a small room, forcing them to be next to each other (and perhaps have no job as well, not sure).
Now it is possible to do this with the military screen, but that's a lot of hassle to set up and work with.
I've found the solution: Screw pumps. I would like to nickname this the 'pump until you screw' room.
Manually screw pumping is a high priority job, and it only takes a few clicks to enable pump operating on your two dwarves of choice.
Screw pumps are really excellent for getting specific dwarves to a place you want them to be.
I set up this room:
WWWWW W - wall
DB>>W D - door
DB>>W B - bed
WfbbW >> - screwpump from west
WWWWW f - prepared food stockpile (no barrels) b - drink stockpile
enable labours on your two chosen dwarves, activate the pumps, once they are both inside, close the doors behind them and deactivate the pumps. They'll have nothing to do but talk with each other, as long as they are adjecent. This setup has a few dwarf position combinations where they are not adjecent, but most of the time they will be talking. The two screw pumps have an added benefit of adding two impassable tiles to the setup (make sure they are pumping from west, so the impassable tiles are next to the wall isntead of creating a barrier in the middle of the room).
Now I don't know if they will also talk with each other when they are pumping, I need to test that. It's not relevant except for hilariousness though. Well, not completely. It would add the benefit of training attributes while dating if it works while they pump.
EDIT: it doesn't look like it works while they pump, they really need to be on 'no job'
EDIT2: interesting observation: the relations not only lists the 3 friendship terms from top to bottom (friends, friendly terms, passing acquaintance), but also the subgroups themselves are ordered top to botom from best friend to least best friend. You can see the relations rise in rank when you monitor dwarves in the dating booth.