It wouldnt make it weak, and some do use a version called a Utility Constrictor. Its basically a single line with the adjustable part just long enough to make the bury to grip the main line.
There are 2 main ways to attach whoopie slings to your hammock.
Larkshead the fixed eye to the hammock...
Larkshead the fixed eye to a ring which is attached to your hammock... (or build the fixed eye around the ring)
Build the adjustable loop around a ring thats attached to your hammock.
The first 2 keep the adjustment point from moving away from the hammock body.