Is the Skyport Plus HS for Nikon also usable on manual when mounted on a Canon? I don't need the Hi-Sync feature, just for triggering.
Yes you can use it manually.
Only the hot-shoe middle contact is available to trigger Elinchrom flash units.
You can use a Canon Skyport HS on a Nikon or a Nikon Skyport HS on a Canon in manual mode. You can still controll power and see the unit displayed on the Skyport HS.
But Hi-Sync and ODS features are not available and will not have any effect!