We also fully support custom domains with a sub-domain other than “www”. So you can use a domain like “blog.mywebsite.com” if you’d like.
From Tumblr’s custom domain help page.
Does anyone know if I can have the tumblr setup on another folder level? As in, rather than it being hosted on www.mywebsite.com, it’s hosted on www.mywebsite.com/sdsblog, and the root site is not tumblr-formated?
Would mywebsite.com/sdsblog be the same as sdsblog.mywebsite.com (in terms of possibility)?