Yes to both the general and specific cases.
Multiple Auras In general:
While unconsciousness will end an Aura, an aura that is not a product of a Stance will be unaffected by other Auras up save through explicit mention of the rules.
There is nothing, for example, to prevent a skald multiclassing as a cavalier to have both her skald's aura up and the defender's aura at the same time. Also given that at least one of those auras is at-will, it can be presumed to be "always up" and does not need specific activation at the start of combat.
An aura is a continuous effect that emanates from a
creature. Unless otherwise noted, an aura uses the following rules.
Fills an Area: The aura fills the creature’s space and each square
that is both within a specified distance of the creature and within
line of effect of it. For instance, an aura 1 affects each square
adjacent to the creature. A creature is normally unaffected by its own
Unaffected by the Environment: The aura is unaffected by environmental
phenomena and terrain, although blocking terrain blocks an aura. For
instance, an aura of fire is unaffected by an area of extreme cold.
Overlapping Auras: If auras overlap and impose penalties to the same
roll or game statistic, a creature affected by the overlapping auras
is subjected to the worst penalty; the penalties are not cumulative.
For instance, if a creature is affected by three overlapping auras
that each impose a -2 penalty to attack rolls, the creature takes a -2
penalty, not a -6 penalty.
Deactivating an Aura: A creature can take a minor action to deactivate
or reactivate one of its auras. However, certain auras have set
durations and cannot be reactivated after they end.
Death or Unconsciousness Ends: A creature’s auras end immediately when
it falls unconscious or dies.
Bard and PP Feature
The Skald's aura is an aura produced by the class utility power and governed by the aura rules above.
The "Aura of Peace" is a class feature. It is not an aura and obeys none of the rules for auras because it does not have the aura keyword and because it is not a power. It just works.