Kunze, 220.127.116.11, discusses what you reference, Martin, that the real problem is getting the zinc into the wort, as 80% is lost in mashing,* as well as some remedies. As for Servomyces, it is yeast, but grown on an exceptionally zinc-rich medium, so that tiny amounts provide plenty of bio-accumulated zinc, avoiding the problem of off flavors from the amount of normal yeast slurry you'd have to boil to provide the same amount of zinc. (I use it, as I mentioned above, when I for whatever reason only want to supplement zinc, as when using carbon filtered tap water. When I use RO, and in starters, I'm more inclined to use Wyeast nutrient because I figure other trace elements may be deficient. I should probably stop making this distinction and save money.)
*Briggs, et al., Brewing Science and Practice p. 164, puts the amount of zinc from malt that makes it into wort at just 5%, and notes that much of this is unavailable to yeast because of chelation etc.