From the SRD
Holy Avenger
In the hands of any character other than a paladin, this sword performs only as a +2 longsword. In the hands of a paladin, this holy (+1d6 points of bonus holy damage against evil creatures) becomes a +5 longsword, creates a spell resistance of 15 in a 5-foot radius, and casts dispel magic (usable every round as a standard action) in a 5-foot radius at the class level of the paladin. (Only the area dispel is possible, not the targeted dispel or counterspell versions of dispel magic.)
Caster Level: 18th; Prerequisites: Craft Magic Arms and Armor, holy aura, creator must be good; Market Price: 120,315 gp; Cost to Create: 60,315 gp + 4,800 XP.
The rogue would use it as a +2 sword. He is not a paladin even when he is emulating a paladin class ability. No matter how he argues it, the question still returns to Are you a paladin? The answer is no. therefore he can't use it. Neither bluff nor umd will alow him to use the item other than a +2 weapon.
Same thing for the Druid Vestments.
From the SRD, please note thee bolded section. THAT applies to holy avenger and druid vestments with respect to a rogue trying to bluff his way to use an item.
The rogue is simply asking too much off the target, whether the target is intelligent or not.
Assuming the holy avenger or druid vestments aren't intelligent, the the bolded Italicized section applies.
And since both items are NOT creatures. The Rogue can not use the items as if he were of the appropriate class.
(*)Bluff (CHA)
Check: A Bluff check is opposed by the target's Sense Motive check. Favorable and unfavorable circumstances weigh heavily on the outcome of a bluff. Two circumstances can weigh against the character: The bluff is hard to believe, or the action that the target is to take goes against the target's self-interest, nature, personality, orders, etc. If it's important, the DM can distinguish between a bluff that fails because the target doesn't believe it and one that fails because it just asks too much of the target. For instance, if the target gets a +10 bonus because the bluff demands something risky of the target, and the Sense Motive check succeeds by 10 or less, then the target didn't so much see through the bluff as prove reluctant to go along with it. If the target succeeds by 11 or more, he has seen through the bluff (and would have done so even if it had not entailed any demand on him).
A successful Bluff check indicates that the target reacts as the character wishes, at least for a short time (usually 1 round or less) or believes something that the character wants him to believe.
A bluff requires interaction between the character and the target. Creatures unaware of the character cannot be bluffed. A bluff always takes at least 1 round (and is at least a full-round action) but can take much longer if the character tries something elaborate.
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