The short answer is yes.
Deer feed on many things including aquatic plants.
These are plants the deer were eating.
The seemed to be eating the broad-leaf plant pictured here. As I observed them feeding there were times when the does would submerge their noses and come up chewing a lot of plant material. Leaving the impression they may have been consuming all the plant material.
It is easier to list the things deer do not eat than to list the things they do eat. On a couple of occasions I’ve witnessed deer eating dead fish. In one case a deer caught a stranded 6-8″ sucker chewing it from head to the tail much the same as they would chew an ear of corn.
These deer stayed and fed on water plants for a long time.