I remember an issue discussed about in the Ihya I cannot recall if its in the Ihya itself or the Sharh but the gist is as follows: What if a corrupt king who spends his money and time on corrupt activities decides to grant monies to build a Musjid, is it allowed to accept his money? The rulings given are as follows: That at least those monies will not be spent in corruption thus it will be deemed permissible to accept the funds but if the king is doing this to show that his rule has the acceptance of the pious and if the acceptance of the funds is seen as an endorsement of his corruption it would be impermissible to accept the funds. In my humble opinion I feel the same would be applicable in this situation. Those in favour of sitting with deviants at a gathering or on their platforms such as radio,TV, and places of worship could present the argument that at least for those moments the people would be saved from the utterances of a deviant but the greater danger is that in the eyes of the general public this act could be seen as an endorsement of their deviance. Albeit there has been instances in the past where righteous scholars openly and publicly rectified any incorrect utterance or mistakes made by any other speaker at a gathering.