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While a 2B technically allows for a waiver if a branch wishes to grant one, right now you'd have two issues. First, no branches are offering waivers because there is an abundance of applications being submitted but fewer jobs to fill (due to budget cuts to the military). Second, drug offenses are one of the last offenses waived by the military.
As for your second question, your separation and NJP, while not a conviction, is still evidence of an infraction on a background check. They don't need a conviction, but rather, facts and circumstances that indicate an infraction occurred. Unfortunately, it is not illegal or unauthorized for them to consider that offense when deciding whether or not to dismiss another potentially chargeable offense.