Damn Sylvain, keep talking like that and you'll obsolete half the posting on BGG.
However, you've mis-predicted in this case
page 15 wrote:
While monster attacks cannot target or affect a knocked out hero, hero players may only target a knocked out hero with an ability that would allow the knocked out hero to recover any amount of damage. For this exception, the knocked out hero’s hero token is treated as a hero even if another figure occupies the space containing the hero token.
So no, I don't think Tomble can hide under the body of a fallen ally