Here's another thought:
Don't use visibility calculations to try to connect nodes, use the movements of human players. As humans are moving around, maintain a list of the nodes the human was at in the last 5 seconds. Before nodes can be considered candidates for connection, they have to both be in a human player's "nodes I visited in the last 5 seconds" list. If a player is at node #785 and moves to node #819, add 819 to node 785's list of "nodes I can move to from here". And make a note of whether or not the human jumped or crouched when moving from 785 to 819. If humans only ever move from 785 to 819 while crouched, that should be a good clue bots need to do likewise. That would eliminate the major problem with cs_militia where the CT bots spend most of the round trying to walk through the fence by the sewer tunnel entrance.

As to the steep slope thing, simply add enough nodes so that they are within the connection limit tolerance. That way, if I'm walking up a steep slope, legitimately connectable nodes would be added frequently enough so that they will be within the vertical connection checking limit. One other thing, it wouldn't be necessary to do eliminate nodes below current position if they are water nodes, since falling into water doesn't cause damage.

Oh, one other thing, when a bot decides to camp, make them do a "am I on a ladder" check like they do a "am I under water" check, so they won't camp on ladders. Camping on a ladder often blocks other players from being able to go where they need to go. You can't shoot accurately on a ladder, and your ability to take cover in a ladder is quite limited, so ladder camping is something no intelligent human player ever does. It would be greatly appreciated if the bots didn't do it either.