Being a Dylan and Dead fan, I can only guess, but here goes: I think there is disdain for the Dead in Dylan circles because Jerry was a bad influence on Bob. Having been on tour and seen all the Dylan/Dead shows, I was SO looking forward to their collaboration, but thought it was muddled at best. It was better without Petty, but still not what I was expecting. I prefered the rehearsal tapes I had to the actual shows (does anyone have them on cd??) Dylan put on some of the worst shows of his career from about '85-'93 and then something happened and he started to actually care and his shows became incredible to watch again.
In a Dylan biography that I read, Dylan actually asked to join the Dead, but Phil said no! As for their connection, Jerry idolized Bob the way many folks do. They respected each other as musicians and songwriters and both had a love of music that goes way beyond us mortals.
"The only funeral you should ever try to interrupt is your own, and that should be a full-time job." -Kinky Friedman