I asked five publishers (two online and three print) that question and the answer is YES.
Admittedly, the editors I asked at the AWP book fair were surprised at the question. I was left with the impression that they do not have a policy in place. In fact, I'm not sure how often the question comes up. Unless a poem has been previously published on an online journal or in a print publication, it is not considered published if it is on a blog.
One editor said it was the equivalent to me, for instance, printing out a poem from my computer and handing it to a friend. Is that considered published? Technically yes, but it doesn't count. That same editor asked if my blog was a popular blog ... so if I had a high readership, would it be worth it for an establish publication to pick up the poem?
These five publishers are not the be all-end all when it comes to submitting work (and I'm not naming names, though tempting). But there is a lot of gray area that hasn't been defined. I say--take advantage of the gap and send out your blog poems. Just be sure to double check each publisher's submission guidelines.