The problem you face is not that easy. You do not know why that person has been DFd, unless you were in on the JC, and if you were, and agreed to the DF, then you would likely shun them.
Not knowing the reasons behind it, your safest thing to do is shun. For all you know, that person has gone the "A" route and could drag you right along.
Getting DFd takes effort. There are cases of unjust DFing, but you won't know if this is the case (more than likely). In most cases, however, a DF requires quite a blatant disregard for the JC, as the JC is usually reluctant to DF. So, if the person was DFd, they more that likely told the JC to take a flying leap.
And, is that the kind of person you want to be associating with?