@Nina:
That is a great question. I'd have to say that Blizzard will not be happy with this technique- and here's why: it's an abuse of game mechaninc- or rather, a flaw in game mechanics.

The intent for the holiday bosses is for max level characters to be able to Q for them. Hence, the only way to queue for them is through the LFD system. Remember that Blizzard intentionally removed the bosses from the regular dungeons. Also, The loot tables are clearly not designed for non-max level characters.

All that adds up to an intent for only max level characters to have access to these encounters and rewards. Any attempt to circumvent these limitations (no matter how clever, and that one is pretty clever) will likely be viewed by Blizzard as an exploitation of game mechanics. Players falling into that category tend to have achievements and loot revoked, and possibly warning bans as well.

All that being said, this might fly under the radar. Blizzard may not notice, or may not care and simply 'let it go.' But I think the evidence is clear that the technique is not intended. Others would be wise to avoid it, or at the very least, only attempt it with full knowledge of the possible consequences.