Dots can crit, yes. Otherwise there'd be no sense in BRD's River of Blood trait, which resets Bloodletter when our dots crit 50% of the time. As for the value of crit chance, it gets devalued by certain mechanics across different classes. Straighter Shot procs devalue it for BRD (though RoB boosts the value overall, slightly). Same with Bootshine on MNK and Life Surge on DRG.