Assuming the ratios given to Cliff by the hatchery are accurate, then:
With Hatchery: 708 quarts X 100,000 eggs is 70,800,000 eggs. Survival rate is (low end) 75%, so total fry is 53,100,000. If 10% go back into Vermilion, that's net +5,310,000 new fry this year.
Natural reproduction: 70,800,000 eggs at 3% (high end) survival rate would be net +2,124,000 for vermilion this year.
5,310,000/2,124,000 is 2.5X the walleye fry in vermilion this year compared to natural reproduction.
I'd take a 250% return on pretty much anything!
Ancillary benefit is +47,790,000 fry to other MN waters.
I'm sure there's a downside, but I can't see it.
We got onto the ice down there this winter one time and it was really easy to get on and off of the ice right there. Looked very friendly for boat traffic and the way the rocks jog out to protect the access it is on my hit list if I need to find an access to launch from this summer. If you use google earth you can check it out.