Q:

Does cover also grant concealment?

One of the PC who plays in my Encounters session has a power that lets him make a stealth check to hide if he has "concealment."  Last night we was behind a hard corner in a room without any other terrain effects.  The monsters had their line of sight partially blocked which gave him cover.  So the question came up on whether cover also grants concealment for the purpose of making a stealth check with his power.  This was important to the PC because if he makes a successful Stealth check he gets combat advantage and does more damage.  
I ruled that it did not because even though the monsters would have a difficult time hitting his PC with a ranged attack due to the cover, they could still partially see the square he was standing in as he was trying to hide.

A:

No, cover and concealment do not normally influence each other.
Cover and concealment are different properties.
Cover is derived from interrupted lines of effect:

The target is around a corner or protected by terrain. For example, the target might be in the same square as a small tree, obscured by a small pillar or a large piece of furniture, or behind a low wall.

Concealment is derived from obscured terrain:

Lightly Obscured: Squares of dim light, foliage, fog, smoke, heavy falling snow, or rain are lightly obscured.
Heavily Obscured: Squares of heavy foliage, heavy fog, or heavy smoke are heavily obscured.
A creature has total concealment when it is in a totally obscured square. Example: Total darkness.

Therefore, hiding directly behind a corner may be sufficient to give a character cover, but there's nothing preventing monsters from perceiving that character in that square. However, if it's in a darkened corner, there may exist low-light in the square as well as physical obstruction. Both interrupting line of effect and having some condition that worsens visibility.
Most stealth checks require:

A creature can make a Stealth check against a target only if the creature has superior cover or total concealment against that target or if the creature is outside the target’s line of sight.

Which a darkened corner would not normally grant, save for special cases like the Shade race.

