Actually no, not all skin tags are from hemmies, there are skin tags that are from crohn's and they are very different then hemmies...see this link...
http://www.emedmag.com/html/pre/fea/features/011504.asp
The first set of pics are hemmies, the set of pics below that are perianal crohn's skin tags (related to crohns disease only), any UCer with skin tags should be checked by a good colon and rectom surgeon to ensure they are hemmies and not the crohn's skin tags...my skin tags were misDX as hemmies and during a bad flare (which I didn't relalize at the time that that is what it was) they were banded like they do to hemmies and that was a huge mistake.
Never make assumptions, find out for sure.
:)