Summoned pets can add a great deal of DPS to the raid, but they can also cause severe problems if they are not used correctly. All pet owners will thus need to pay a lot of attention to their pet, to make sure the pet's presence is not detrimental to the raid.
The pet owner will primarily need to make sure that the pet will not attack any monsters when they should not be attacked and that the pet will attack the correct monster and only that one. This is especially important during pulls and when the monsters posses some kind of AE effect that will aggro pets. A pet that charges a monster being pulled after the monster casts an AE spell can easily wipe the raid, because the pet may aggro the monster's friends. A pet that is attacking the wrong monster will make it much more difficult for a tank to move the monster to the correct position. A pet that is attacking from a bad angle (i.e. mostly not from behind) will probably be hit by ripostes and thus waste the pet owner's or healers' mana, because the pet will need heals or the owner will need to cast a fresh pet after the old one dies. A pet attacking from a bad angle will generate unwanted push in a bad direction. A pet that attacks a monster before rampage is set will move the pet owner on the rampage list.
Pet control is much easier with the /pet hold advanced ability - although the owner still needs to pay attention to what the pet is doing. This ability will allow the pet owner to make the pet not attack unless the owner asks the pet to do so; this allows the pet to ignore AEs and it allows the owner to call the pet off if needs be. It's a good idea to use /pet hold at the beginning of the raid and then again after the raid kills any of the monsters; that will make sure that the pet will not interfere with other monsters unless the owner asks the pet to do so. Generally, it is considered a bad idea to use a pet on raid if the pet owner does not have the /pet hold ability; the important thing however is whether or not the owner can control the pet. If they can, there will be no problem using the pet even without the /pet hold ability, and on the other hand if they can not control the pet even with /pet hold, the owner will be asked to kill the pet.
All of this applies to all kinds of pets, including swarm pets. The rules are the same - if the owner can make sure the pet will not misbehave, there will not be a problem using the pet, and if the owner can not make sure the pet will do exactly what it should be doing, the pet should not be used. All other things mentioned in this guide - including melee positioning and shrinking - apply to pets as well.
I think that in the past pets were one of the two bigger problems on raids in our guild (alongside with broken mezzes), so we will need to concentrate on making them work better (especially to keep them on a tight leash at all times). When used correctly, pets can be a great help to the raid because of the DPS they can generate - so we should attempt to improve in their handling; it will be a great help in the long run.
Using charmed pets (including dire-charmed ones) on raids is generally a very bad idea, unless the raid leaders says otherwise. The pet will go loose if the owner invises, dies, or when the charm wears off prematurely - and a loose pet among the raiders is not worth it.