This site does have it's own PGN Viewer/Editor - Game Editor. You can find it in the pop-up menu on the 'More' button. You sound as if you know your way around the nuts & bolts of chess sites but this may help...
http://support.chess.com/Knowledgebase/Article/View/148/2/how-do-i-use-the-analysis-board--editor
Don't know anything about the blogging site you mention but Game Editor will let you embed a diagram or game in another website. It does this by providing you with the HTML code you need to create a link to the archived game on chess.com (but from the other site).
I've tried embedding a game into my own webpage & it worked perfectly with all the functions of one on this site such as stepping through moves.
Hope that helps.
I want to embed my archived PGNs on this site to my blogger blog. Currently I am using a third-party pgn widget to do it, but I was wondering if Chess.com has its own pgn viewer for external use.