It is not possible to directly "embed" a Tumblr or WordPress blog into your SupaDupa boutique, as neither of those services support framed embed options, and their is no option on SupaDupa to support embedding in such a manner either.

What you may be referring to by the word "embed" is having a blog on another service and making them look the same. An example of this is a SupaDupa user AnyForty, who has their SupaDupa shop at http://www.anyforty.com and their Tumblr Blog at http://blog.anyforty.com

It is important to note that in the example case above, the blog is NOT embedded, but remains hosted on Tumblr. The "blog" sub-domain has been pointed to Tumblr to add cohesion to the brand, neither of which have anything to do with SupaDupa.

The reason they look the same is that in this case AnyForty had hired someone to customise the HTML & CSS of their TUMBLR blog to appear similar to their SupaDupa boutique.