Chapo are shock jocks
who use vulgarity as a political tool but are entertainers, not political leaders. Combine Howard Stern's vulgarity, Jon Stewart's political comedy, and socialist politics and you get them. Add dudebro ironic memers and you get their fans. While they have coined the term Dirtbag Left them and their fans are just one crude expression of those particular politics and even they are not actual bigots. What I know of them is based mostly on their appearances outside their own podcast (their vulgar humor is not my cup of tea) but I took time to do some research after reading this thread since the reactions here were so extreme. And yes, they do cross the line sometimes. Namely, when using humor that makes light of sexual violence which they have apologised for. Otherwise I don't see bigotry, only vulgarity that occasionally crosses a line like such humor has a risk of doing. The instances of rape humor I condemn unequivocally but that is not the totality of their content and it seems to be limited to few instances that they have apologised for and donated to charity as a gesture of repentance.
Which one is worse? Installing and defending racist policies that destroy people's lives and probably killed many or making violent shock jokes about a person who has done so? Questioning priorities of liberal politics is at the center of their performance. You can be a bigoted white supremacist (Bloomberg) or a war criminal who has caused thousands of deaths (Bush jr.) and still be an accepted member of high class society but make vulgar, disrespectful jokes and you are a lunatic. I didn't find instances of them promoting violence against a vulnerable group of people or dehumanizing a such a group which is the type of "ironic" humor that encourages bigots to violent acts. While their brand of humor does not appeal to me personally, I think it is ridiculous to compare them to alt-right. And yes, if there is a violent plot or act inspired by them I will reconsider my opinion.
I see Sanders campaign touting Joe Rogan's endorsement as a bigger blunder than the campaign members appearing in Chapo. While Rogan's bigoted views had nothing to do with the endorsement he still is a bigot. Chapo are not as far as I can see.
What is the ideological ground Dirtbag Left stands on? Criticism of the liberal hypocricy and white upper class feminism is an integral part as is the emphasis on class politics. Claiming that they ignore identity politics is a strawman, though, class reductionism is also seen as harmful since class and identity are intertwined. Turning identity politics into a tool for class oppression actually harms vulnerable groups since they are disproportionally working class instead of upper class and class reductionists' blindness to bigotry shuts down minority voices within working class. There is a constructive dialogue among leftist activists (both "Dirtbag Left" and "SJW left") about where is the line on eather side where you start doing more harm than good and how to combine different approaches. The disagreement isn't on goals, it's on tactics.
From a personal experience I can say that lurking around in spaces many of which fall under the definition of Dirtbag Left has taught me about minority issues I was ignorant before; namely those of non-binary and non-passing trans people (and conflicts within trans community). It seems trans rights are a current battleground in the culture wars and the online left seems to have been unified in that fight. Again, there is disagreement about means and long term goals (gender abolition or not?) but the short term goals are common: equal rights for trans people of all kind.
And how do Dirtbag leftists relate to Bernie Sanders? From what I have seen, while they meme about him their feet are on the ground more firmly than I would have expected. Their politics that usually are far to the left of him, so they see him as a figurehead to be used, not an idol to be worshipped. There is not nearly as much gringy fawning about him as a person as there is for example in TYT.
And is Sanders a bigoted class reductionist?
Not according to Barbara Smith, a (black, lesbian) feminist scholar who helped coin the term identity politics.
I am often disheartened, however, to see support for identity politics and intersectionality reduced to buzzwords. I am supporting Bernie Sanders for president because I believe that his campaign and his understanding of politics complements the priorities that women of color defined decades ago.
Edit: Oh, I forgot something important: when it comes to Dirtbag Left and fight around it it's very much an online phenomenon. It is important to note that it is only a part of leftist activism sphere and most of the real work is done offline. Go to an average grassroots activist offline - whether connected to Sanders campaign or not - and there is a good chance that asking about that kind of issues gets you a confused stare.