Good news: He has a good enough fishing set up and can get out on the river and get into some fish. It is true that the fish don't care what type of rod, reel, line, etc you have. As long as some type of bait/lure is presented decently (appropriate depth, suitable size and color, etc) and a fish swims past it, chances are they will hammer it. Looking backl to when I started out river fishing I can tell you that my gear was NOT that well suited for the Vedder, but I made it work and even caught some fish! So yeah, don't sweat it, just get out and fish what you have. Can always upgrade later.
Bad news:
-Spinning reel set ups are not that well suited for float fishing. Better suited for casting something out (spinner or spoon) and reeling it back in. Of course you CAN float fish with a spinning reel, it's just hard to open the bail and get a nice smooth drift on your float, then when you float goes down quickly close the bail and set the hook. This is much more easily acclomplished with a bait casting (level wind) reel and rod. Or, a centerpin reel/rod (generally not the best idea for a beginner to buy).
-This is a pretty heavy set up for coho. Maybe ok if you hook into a big spring or chum. The rod, reel, line will be a bit overpowering on smaller salmon. Also the set up will be a bit heavy to hold all day, cast, reel in, could lead to some tierd arms.
-With that powerful rod, and braid with no stretch, all lot of "shock" (in search for a better term) gets transferred to that 12lb leader. You run the risk of snapping off fish. However if you go to too heavy a leader, say 15lb, the fish can see it more easily and are less likely to bite your offering.
Here is what I would do it it were my rod/reel: For float fishing tie the braid right to your swivel (float and lead above swivel obviously) and run a 12lb mono leader. If I keep snapping off fish go to 15lb leader. Also try and toss some spoons and spinners with the rod, however tie the braid to a barrel swivel, then 3 ft or so mono leader of that. Not so important if the water is dirty, but if it is clear I believe that braid is too close to the lure and the fish will se it and not like it (spook them).
FYI the typical entry level float fishing set up for the Vedder is something like this:
10"6 baitcasting rod. Somewhere in the 8-17 line rating (I like) or 12-25 line rating (a bit more beef).
Level wind reel (Abu 6500 or whatever)
15-20 lb mono mainline.
8-12lb leader
So, in conclusion, I think the guy a Cabelas didn't really know what he was talking about! But, like I said, don't sweat it, just get out and fish the set up and if you don't like it save it for a more appropriate fishery (say the Fraser) and invest in a new baitcasting set up for float fishing. Final warning, if you have never used a baitcaster there IS a learning curve!!! Some birds nests are bound to happen and frustration is inevitable. However, most things that are worthwhile learning are not easy, and learning to use a level wind adeptly is no exception.