They are? I've got a Fallen Spire game going on an X map where there's somewhere around 20 SF posts behind my main chokepoint. In 10 hours, not a single reinforcement has come in through them.
I'm pretty sure they don't count as reinforce gates, the AI can't warp ships to them like it can to guard posts. They're worth killing if you're worried about the special forces and want to shrink them, but if you have solid chokepoints the SF really don't seem to be that threatening to chokepoint worlds and unless you take out a lot of them that 5% isn't going to matter very much (and if you do take out a lot of them, the AIP starts to add up).
I used to kill them, right now I'm ignoring them unless they happen to be next to a capturable I want to keep (since they'll shoot at it if I leave them).