Wordpress Company bought Tumblr, because it's very active.
I make some sites using a Tumblr theme.
Support has basically stated that I can't share it, because it's too branded, or something.
But yes, you can absolutely make money on Tumblr.
It's a very active soical site, and it's easier to setup a CMS driven site, there, for free, than pretty much anywhere else, I'd argue.
If you can make money with websites and blogs, you can make money with Tumblr.
Best to you...