@Questions21702,
If he is putting the images up on Tumblr, anyone else on Tumblr can reblog them (essentially putting them onto a separate page, e. g. their own Tumblr blogs). But they have to get them from him or whoever put them up first.
Even using HootSuite or a WordPress plugin to add to Tumblr, the posts have to be created and sent somehow. They don't just magically appear out of thin air.