Shared Dreaming is not scientifically proven, but there is alot of studies going on at the moment on this forum.
In my opinion yes it is, simply because the results from the experiments are so good (the amount of similar dreams is beyond coincidence.)
Here are some links to some areas of the forum about Shared Dreaming:
WakingNomads Shared Dreaming tutorial
Official Thread
Shared Dreaming Forum
Shared Dreaming test results page
Hoped this helped, goodluck