Why not? And hammocks themselves can be anchored with teared energy absorber like used in via ferrata mountain climbing — https://en.wikipedia.org/wiki/Via_ferrata#Energy_absorber . This will make the construction much safer than a single two-point seatbelt.

Going to the restroom might prove to be somewhat challenging, though...

If they're anchored correctly, you'd probably be quite safe in a hammock during an emergency landing, in a relative sense - being suspended would absorb a lot of the energy. But agreed, it does seem pretty silly and probably wouldn't feel very safe!!