The Libris Mortis description of the shadow veil item (p76) says it precludes wearing any other kind of armor. Does this include a cloak of charisma or is a cloak not considered a kind of armor?
A shadow veil is a robe-slot item, which interferes with magic armor but not with shoulder-slot items like cloak of charisma. Note its presence in the Undead Armor section of Libris Mortis. See Magic Items on the Body for more information on the various slots and how they are filled:
Many magic items need to be donned by a character who wants to employ them or benefit from their abilities. It’s possible for a creature with a humanoid-shaped body to wear as many as twelve magic items at the same time. However, each of those items must be worn on (or over) a particular part of the body.
A humanoid-shaped body can be decked out in magic gear consisting of one item from each of the following groups, keyed to which place on the body the item is worn.
- One headband, hat, helmet, or phylactery on the head
- One pair of eye lenses or goggles on or over the eyes
- One amulet, brooch, medallion, necklace, periapt, or scarab around the neck
- One vest, vestment, or shirt on the torso
- One robe or suit of armor on the body (over a vest, vestment, or shirt)
- One belt around the waist (over a robe or suit of armor)
- One cloak, cape, or mantle around the shoulders (over a robe or suit of armor)
- One pair of bracers or bracelets on the arms or wrists
- One glove, pair of gloves, or pair of gauntlets on the hands
- One ring on each hand (or two rings on one hand)
- One pair of boots or shoes on the feet
Of course, a character may carry or possess as many items of the same type as he wishes. However, additional items beyond those listed above have no effect.
Some items can be worn or carried without taking up space on a character’s body. The description of an item indicates when an item has this property.
Emphases mine—notice how a robe or armor is separate from a cloak or a cape.
Furthermore, there are rules for combining magical items so that they can be used at the same time. This usually incurs a price premium of 50% for each effect after the first, but Magic Item Compendium specifies that certain bonuses—including enhancement bonuses to Charisma, as found on the cloak of charisma—can be combined with other items at no extra premium, just the sum of the two costs.
First of all, be aware that D&D 3.5e has a thing called item slots. Only the first magical item worn in each slot works.
The three slots for what you would call the torso in plain language are the Shoulder slot (cloaks and capes), the Torso slot (vests and the like) and the Body slot (armors and most robes you wear over a vest, including the Veil).
Armors are worn over the whole body, and this prevents you from using two armors at the same time, but due to how item slots work it could still be possible to wear a nonmagical armor (still providing a bonus to your AC) and the Veil at the same time, weren't it for the wording of the Veil specifically preventing it. Basically, the authors want you to make a choice between AC and the benefits of the Veil.
Now that you can see that the wording is only there for enforcing some regulations over the Body slot, it goes without saying that no, it does not interfere in any way with the cloak you want to use.