What part of the Canyon are you going to?
I was out there in early October.
On the North rim there are pleny of trees for hanging a hammock.
The South rim it depends on where you are, there are usually plenty of trees but in some areas they are not the kind of trees that would work well for hammocking.
Our main trip was in the Grand Staircase with visits to both rims of the Grand canyon. Or plan was to take our hammocks and if no trees were around we would use my MacCat Deluxe as shelter. In the end we ended up taking our tent due to the forcasted temps being down in the 30s at night and we only have enough gear to keep one hammock warm in those temps.
If you are on the North rim there are great camping spots just outside the park on rt 611. If you are interested I can give you directions to an awesome spot we camped in.