I think the Nashbar and winwood forks are probably the same. A number of other cyclocross & hybrid forks used under other manufacturers' names also look a lot like the Winwood.
FWIW, here's what I think:
-I used a winwood muddy carbon cross disc fork on my cyclocross bike. There were no quality issues and it is very beefy (that is, the legs are beefy), BUT, it gave a very harsh ride. If it failed under tandem/disc use, my bet is that the failure would likely occur where the alu steer tube meets the crown.
-The winwood site says it will work ok with a 6" disc rotor. But for tandem use, I don't think a 6" rotor provides adequate stopping power. It certainly won't be any better than canti brakes, and will probably be worse than v-brakes. I use 203mm rotors on my tandem, and my avid mechanical disc brakes really shut things down in a hurry with 203mm rotors.
-I considered using this fork on my tandem, but decided against it. The thought of a fork failure during a high speed brake application is not a pleasant one, and I knew that not only my safety, but that of my stokers' would be involved in such a decision.
I ended up buying Nashbar's steel 700c fork, which has both disc tabs and canti-studs. I also questioned whether it was up to the task of tandem use, but when I looked at it, it was MUCH beefier than the fork on my old Burley.