Wiktionary has it:

1. (transitive, Internet) To blog something previously posted on another blog.

Basically, even if most people wouldn't recognize it, it's technically a word as long as someone uses it to communicate an idea. Some people add to the definition to say that it must be widely used in order to be really recognized as a word, but in that case, the issue boils down to recognition, not the word's status as a "word". I believe it to be used enough to be considered a "word", even by the latter definition.

Wiktionary has it:

1. (transitive, Internet) To blog something previously posted on another blog.

And the Urban Dictionary has another definition, which is mostly downvoted (2 up, 5 down):

a blog whose sole purpose is to post about other blogs

Basically, even if most people wouldn't recognize it, it's technically a word as long as someone uses it to communicate an idea. By definition, as well as grammatically, it is a word. Some people add to the definition to say that it must be widely used in order to be really recognized as a word, but in that case, the issue boils down to recognition and usage, not the word's status as a "word". As to recognition, I think this one isn't too hard to figure out from context, even when one has never heard it before; as to usage, it is uncommon, but all words start out that way. Blog itself was such a word once.