Unfortunately Respawn points CANNOT be controlled via the their Spawn Channel, i.e. via scripting. Alas, there are a number of Forge Objects that, despite having a Spawn Channel, don't actually work with the scripting - I'm compiling a list of them in my Forge Scripting Guide.
Additionally, you also cannot control the spawning of Respawn Points via the inf_flight_reveal and inf_flight_remove advanced gametype labels either. From what I can gather, anything that you can't control its spawning of via scripting, you also cannot control via gametype labels that also control spawning.
Does that mean all hope is lost? Well, not exactly. You can work around this issue. So, how do you control player spawning in infection? Like this...
Teleporters!
Teleporters can be spawned in/out via scripts, but DO NOT use inf_flight_reveal/inf_flight_remove on them! Using those labels produce odd results, which I'm not going to go into detail in here, but sufficed to say, just don't use those labels on the teleporters - it isn't going to work the way you hope it will, trust me. Instead, put inf_flight_reveal/inf_flight_remove on Scripting Timer objects. and have those control the spawning of the teleporters.
To make use of the teleporters as a way of controlling player spawning, only put respawn points in a designated "Spawning Room", and then have a Sender Node that covers that room. Instead of placing respawn points on the map, use Receiver Nodes. You can then spawn in/out whichever receiver nodes you want active at whichever point in the game you want them to be active. The only downside to this is that you won't get the normal "spawning mechanics" you would expect from respawn points, such as spawn weighting, and ensuring players don't respawn too close to other players - so bear in mind this limitation when deciding to build a map/gametype around this mechanic.
If this still doesn't make sense, I can go into a more detailed, step by step, example if you require.