As Talon mentioned, the server has to already have co-op maps in the rotation for them to be voted.  The voting menu does not indicate what mode a map is, however.

I can't easily make the server vote setting work with only one player.  I can do it manually, however every time I make a change to any setting after, it will reset the vote min limit to 2. The thing you're thinking about with loading a new map, Funko, is what happens when you have the minimum players needed to for the round to START is at 0 or 1.   When the amount of players falls below the minimum, the server waits about 10 seconds, and if no more players have joined, it will act as if the round is over, and move onto the next.   I am not willing to put min-players any lower than 2 on the BI server, as having it as just 1 means that a single person can sit and capture all the CPs in a map before any enemy has even joined the game.

Has the BI server been down since yday or is it just me?

So in answer to your question, no because there is no specific mode, it is the map that determines whether it is co-op or not. The annoying thing is that in the map vote both the co-op and conquest version of the same map looks identical, so it is pot luck whether you get the co-op or conquest if both are in the rotation.