Yes, sitcom can be considered an acronym.
The ODO definition is a bit too restrictive, if you ask me.
Compare it to the OED, which has two distinct senses of the word: the first is identical to initialism (i.e., when each letter in the acronym is pronounced individually); the second is:
A word formed from the initial letters of other words or (occas.) from the initial parts of syllables taken from other words, the whole being pronounced as a single word (such as NATO, RADA). [My emphasis]
The Merriam-Webster definition is also more inclusive:
a word (as NATO, radar, or laser) formed from the initial letter or letters of each of the successive parts or major parts of a compound term
Both these definitions tally with the very first two sentences in the Wikipedia article on acronyms:
An acronym is an abbreviation formed from the initial components in a phrase or a word. These components may be individual letters (as in laser) or parts of words (as in Benelux and Ameslan).
All this does not mean that ‘acronym’ is the first thing people think of when they hear sitcom—it is an option, but I would not call it the ideal description. Sitcom is a more typical case of blending, so if you are simply looking for a word to describe sitcom (rather than specifically wondering whether you can describe it as an acronym), I would use that instead.