So long as the tarp isn't depended on as a primary shelter, I'd think it would work fine. I grew up in SE Alaska, and at least once a year the winds would hit up to 150 mph, though not very often in spring/summer. I'd hate to see what the weather could do further north or at high elevations; I don't know where your friend's race will be. That place is large enough to encompass 3 or 4 different climate regions. I think a bivy would work fine, and unless the trip is going to be during summer, I don't think I'd trust a 3-season shelter for extended trips. A 4-season rating is called for in that case.
Oh, and I usually like potatoes, salmon berries, or dried salmon to go with fish oil. You have to go pretty far north to find people who use whale or seal oil.
One more tip: For Southern-Southeast Alaska during 3 seasons, my rule of thumb is to figure that it's about 10 F colder and twice as wet as the Northwest lower 48. I don't know how much that helps. I usually err on the side of preparedness whenever planning a trip up there.