Well, I think musically they're unconnected as far as their styles, but both did use punk as the jumping point to whatever style they themselves embraced or developed (Joy Division with a marriage of Glam drama and more classic rock elements from the early 70s with post-punk angst, Nirvana with a hybrid of heavy metal pre-MTV and an appreciation of psychedelic and Sixties pop).
I would say that if Ian and Kurt really are connected, it's in the sense that they were too sensitive to deal with the varying degrees of fame thrust upon them (Joy Division never got the kind of ink Stateside as Nirvana in their heyday). Both suffered physical ailments that were either heightened or caused by the pressures on them (Ian with epilepsy, Kurt with a debilitating stomach ailment) and both would seem to have been trapped in their marriages (I'm just being hypothetical with Kurt; he may well have been going through the same depression over his love life as Ian, but we don't know. There's really nothing to suggest Kurt and Courtney were headed for a break-up, as far as I've read).Both left behind a wife and young child with many questions as to why they had to leave, so in that sense they are alike.