Zack, thank you for sending the screenshots and providing additional information. The MozBar is showing a domain authority of 98 because it is still part of tumblr.com, which all sites on tumblr will also have. The snipet of code is linking to an image (which appears to be broken or not loading for some reason). You can see this from the "https://seo-kansas-city.tumblr.com/, and the code looks similar for the links on the image posts. (not showing "nofollow" or Javascript redirect).

These links are not showing up in my Moz Pro campaign tracking or Open Site Explorer either, but that does not mean they are not being seen or giving any value to Google. If you ran a backlink analysis through Ahrefs, Open Site Explorer, Majestic and SEMrush, you will usually get 4 different numbers for both total backlinks and linking domains unfortunately.

What I came to the conclusion of for myself as an answer is that this can have SEO value through images with links, but it will not be a silver bullet. I am also yet to see a Tumblr domain link show up from any of the backlink analysis tools I mentioned, although the coding looks like it is "dofollow". I would love for Takeshi Young or a Mozzer to jump in on this if possible.

Hi Zack, great question, I was actually looking into the relevancy and usefulness of Tumblr a couple months ago myself to see if it still had any benefit SEO wise. The links in tumblr posts are no-follow to my understanding, with the exception of "image posts" that have a link embedded in the image, which Takeshi Young explained in a comment response on his "How To Use Tumblr for SEO and Social Media Marketing" article originally posted in 2013. His comment response was from 2016 which makes me think links within the image of "image posts" on a tumblr blog are still do-follow and have link value.

With all that being said, I do agree with Andy that their are probably better ways to gain links and increase your SEO efforts. If you do give tumblr a try, make each post unique and helpful, and use image posts with relevant links embedded in them.

Here is The Moz Blog Post I referenced: https://moz.com/blog/how-to-use-tumblr-for-seo-and-social-media-marketing. See Enrique Ruiz Prieto comment on this post for the context I referenced about Tumblr image post links.

Adding .html to the end of your URLs is not necessary and causes URLs to look less readable in my opinion. In taking over the site, definitely make sure to do proper 301 redirects and run a broken link check on it as well.