The idea that Bernie and his supporters aren't true Democrats is both insulting and counterproductive.
First off, Bernie Sanders is an independent, he describes himself as a socialist democrat but he is officially an Independent Senator of the US. I haven't said he wasn't a progressive, I am not sure what the term denotes it has been thrown around so much, usually towards Hillary supporters in a negative way.
Second, I don't want to exclude anyone and I sure as the world have no authority to count or not count your votes. Bernie Sanders chose to join the DNC and count himself a democrat, he has that right and I respect it.
It is better for the democrats that he did he so as we have seen when Ralph Nader ran as an independent, it took votes away from Gore. Since Sanders has run as a democrat, when the democrat nominee is finally picked, there will be no Ralph Nader taking votes away from the winner of the democratic party in the general. So, I am glad Bernie ran as a democrat.