Well, the first few bosses in Naxxramas (spider wing, Razuvious, Noth) were not that hard, to the point that scrub guilds that never beat C'thun would farm those encounters after a few months, so I suppose it's possible, but even those guilds were fairly serious about raiding, so I find it very hard to believe that they'd tolerate even one moonkin healing. And they certainly never got past Patchwerk if it was the case.