I carried a Leatherman tool with me on my first Camino in 2013 and traveled by rail from Paris to SJPDP. I kept the tool (which had a small knife blade) in my pack and had no problems. I never had the tool in a carry-on bag on flights, and it stayed in my pack which was checked-on. I don't recall having any of my possessions inspected prior to boarding any of the trains from Paris to SJPDP. In the end I never had any use for the Leatherman tool and it never left my pack, but I suppose it could have come in handy to repair equipment, or slice cheese or chorizo (I always managed to find a kitchen knife in the albergues for that). It did not have a corkscrew for opening wine bottles, which basically rendered it useless....
My second Camino this year I carried no knives, but did have a corkscrew and a "spork" (very useful).
If you have any concerns, just buy a small, cheap knife when you get to Spain. That way if it's lost or confiscated by "da man" no big deal. Just make sure it has a corkscrew on it.
Buen Camino and "Gig em".....