Yeah, a tent peg holding a hammock? Not unless you live on the moon or the forces of gravity are temporarily interrupted. A tent will barely hold my asym tie-downs and won't hold my tarp (depending on soil).
Also, compare that to a 2x4 which the guys have already advised against. Personally, I think the bracket would be easy to make - only an hour's work as long as you have an off-cut disc and a welder. Why not try the 2x4 and if it fails do a 4x4.
I really like the bracket - the whole thing dismantles and packs flat.