Until recently hosts with AUv3 plugins on iOS had no real side chain possibility and therefore Woodpressor, WoodnGate and Woodulator had their own side chain mechanism.
But with the recent release of AUM, real side chaining is now possible and support for this was added to Woodpressor, WoodnGate and Woodulator.
Woodpressor and WoodnGate use the side chain audio to calculate the compression amount or gate triggering.
Woodulator uses the side chain audio as modulation signal (delay and pitch amplitude, pitch frequency, panning, etc). Woodulator also added a side envelope mode which is often more useful for modulation purposes.