https://www.wikitree.com/wiki/Help:Sources
A source is a source. Wikitree procedure as I have long understood it (eight years now) and to me seems clear from the Help page linked above, is to call any source of information, even a blog or a website or my grandma's memory, a source. No judgment as to quality as to whether it can be referenced.
Of course we all want primary and secondary sources to be properly cited when available, and better sourcing is what we strive for. You would want to pull out references to secondary sources linked on your blog whenever possible.
If you are working from a blog post (and there are excellent genealogical and historical blogs out there, just as there are sloppy ones,) you can absolutely cite the blog, including whatever sources they used as well in your citation.
edit--if you are worried your blog might disappear, have you added individual pages to the Wayback Machine?