This page gives a list of 58 members of the 'Congressional Progressive Caucus' (soon to be 57; Cynthia McKinney's in there), who the DSA claims is working with them; but there's no mention of any members of CPC being also members of DSA.
Let's be careful about what we're claiming.
http://www.dsausa.org/pc/pc.members.html
Also, this link is to the "Progressive Agenda". (keep in mind, this is the dem socialists of America's web site). Sure sounds like socialism to me. You ask any lefty and they'll tell you that "progressive" is the code word nowadays for "socialist". It's just that simple. They change their name and suddenly they're invisible. But they're socialists, make no mistake about it.
Technically you're right, they're only 'working with' the DSA. However our reaction to House members being associated with such a radical group that professes policies so anathema to our Constitution should be outrage!
Ask yourself what would be the left's reaction to a website list of republicans who were 'working with' the KKK or any other such radical group? There would be a call for resignations from coast to coast!
You cannot 'work with' DSA and still uphold your oath to the US Constitution, period.