100% yes.
Since I started using one, and putting in basic reps of triangles, armbars and kimuras every day (plus a set amount of time to just experiment and chain ideas together), my game has noticeably improved.
Just in case you give a shit, I made my own - after a thread on here inspired me. I took an old hoodie, gaffa taped a boxing glove into the hood, rolled up a large towel and fed it through both arms, then just padded the rest out with old clothes, then sealing the sleeves and bottom of the hoodie with gaffa tape. I couldn't be arsed making the legs, but the torso is weighty and sturdy enough (I packed it out with a shitload of clothes) to provide useful drilling.
Someone on that other thread pointed out how hard it would be to find a partner willing to drill a technique 100 times on a regular basis. Not such a problem with a grappling dummy.
Nice setup for a practice dummy. Chinese Wooden Dummy was developed for the same reason. "It never complains, it never gets tired and it is always ready to practice when you are" is the saying we had about it in Kung-fu.