There have been toxicities associated with eating daylilies, both animal and human. This would be primarily in Asia and therefore related to species (diploid) daylilies. Usually it involves the roots but doesn't appear to apply equally to all daylily species. If you want to read more about this try a Google search on the word "hemerocallin". Edit: Google will probably ask you if you mean Hemerocallis instead but don't fall for that :-)
The "ditch lily" (Hemerocallis fulva 'Europa') as discussed in your link above is neither diploid nor tetraploid, it is triploid.
