I really didn't want to get into this pissing contest but..........
Look, plain and simple, you can fist a 3wt on the Vedder if you want, its your call, there are no regs that state that you must use a 7 wt while fishing on the Vedder. Now, that being said, for the health of the fishery, I suggest that if you are going to be fishing a 3-6wt rod, that you use a lighter tippet so that the larger fish can be broken off. Again, when fly fishing for Steelhead, you are normally using larger patterns with larger hooks than you would be using when going after cutties.
I fish the Vedder quite often using a 4 or 5wt rod, but I also don't use size 6,4,2,0 hooks and 10-15lb tippet. I use smaller size 14, 12, 10 flies and 4-5lb tippet. If i get B.S Lucky and hook into a Steelhead while chasing cutties, i will point the rod at it, and give it a pull snapping it off. If you are using the correct tippit and correct size hook, you will snap it off close to the fly and the fly is of such a small size that it will not interfere with the movement of the Fish. Also, many times when breaking a smaller fly off in a smaller fish, the fly will fall out rather quickly.
I don't like the fact that there may be a Steelhead swimming around with my fly in it's yap, but it is better than the alternative, playing it half to death. I fish for EVERYTHING, and I mean EVERYTHING, so i just make sure that i use the correct equipment for the species that I am targeting. With the opinions of a few here, they are saying that you should not be fishing for cutties, Bows, etc....with anything less than a 7wt because there are Steelhead in the system, so that means when the Pinks run (I use a 6 wt) I need to use a 9wt because there are Springs in the system at the same time?
Besides all that, when chase cutties on the Vedder, I sure the hell ain't going to the same places I chase Steelhead!!!!
Learn to know what size rod to use with the appropriate tippet and fly size to target the species you are after and all this can be avoided. USE COMMON SENCE!
I want to protect the Steelhead as well, but having a small cuttie fly in it's yap is no worse than having all the hook pricks from missed hookups and "Wild" Steelhead releases!!
Just my 2 cents