No. Walkers and jumpers do not help a baby learn to walk. Walkers and jumpers are ok to use under adult supervision, and for less than 30-60 minutes at one time. They are not for keeping a toddler in, without supervision. Dangers include crashing into furniture corners, flipping over, falling down stairs, and sliding through the seat (possibly getting tangled up and possibly getting choked).
No. They absolutely do not. In fact, walkers are dangerous and associated with more accidental injuries. The best thing you can do to help your child learn to walk is to give him plenty of floor time, initially tummy time, then scooting/crawling time. This should be in a child-proofed area where you can let him roam free with sturdy furniture to pull up against.
No. Jumpers are pure fun for your baby, as most of the time, "jumping" up and down is a pure motor reflex within your baby's legs. As kids get older, they can actually jump actively, but there's no correlation with walking. Baby walkers are dangerous, so much so that they've been outlawed in many countries, like canada, due to safety concerns and fears that they delay walking. Do not use them.
No. Although they do provide entertainment for your child, and free your hands for other activities, walkers and jumpers do not teach your child to walk. The main reason is that your child is not bearing all their weight or balancing themselves when in these devices. Better activities include holding your child's arms or hands while they are standing or a push toy they can hold onto while standing.