Is hollow point ammunition worth the buy? Will they do more damage then standard ammo?

Alright. Short answer: It depends on your target.

Long answer: Fallout: New Vegas utilizes multiple types of ammunition, with varying degrees of effectiveness vs armored and unarmored targets.

Assuming your weapon is Ratslayer(base DAM 23), and your target is either wearing Combat Armor(DT 15) or nothing, here's how it works out:

5.56mm round: does not modify weapon dam. 23 -15 = 8 vs armored target, 23-0=23 vs unarmored.
5.56mm, armor piercing: -15 target DT, -5% weapon DAM. 21.85 -0=21.85 vs armored target, 21.85-0=21.85 vs unarmored.
5.56mm, hollow point: x3 target DT, +75% weapon DAM. 40.25-45=-3.75 vs armored target, 40.25-0=40.25 vs unarmored.
5.56mm, surplus: +15% weapon DAM, +200% weapon degrade. 26.45-15=11.45 vs armored target, 26.45-0=26.45 vs unarmored.
5.56mm Match Hand Load(GRA): +15% weapon DAM, -35% weapon spread: 26.45-15=11.45 vs armored target, 26.45-0=26.45 vs unarmored.
.223 round: -10% weapon DAM, -20% weapon degrade. 20.7-15=5.7 vs armored target, 20.7-0=20.7 vs unarmored.

As you can see, Armor Piercing is just better when you run up against a heavily armored target, whereas Hollow Points inflict vastly greater amounts of damage when the target is not armored. Surplus, Standard, and .223 are just different approaches to being the go-to ammunition. Match is the sniper's golden boy of GRA. Grab Living Anatomy(Lvl 8, 70 medicine) if you want to be able to determine on the fly what ammunition you need.

Taking this into account, Hollow Points are well worth the money when you intend to go up against unarmored or very lightly armored targets. Fire Geckos, Green geckos, Cazadores, Nightstalkers, and the Legendary Cazador/Nightstalker/Fire Gecko are all examples of useful applications for hollow points.

Hollow Points are also, through a bunch of math that I don't understand but .46 ACP does, infinitely superior for Sneak Attack Criticals than any other type of ammunition in existence.

-Nukeknockout

Its simple really Nuke. Critical hit damage bypasses DT/DR (base damage is still affected). Take the Paciencia. The overwhelming amount of critical hit damage with Just Lucky I'm Alive and Better Criticals far exceeds the penalty for extra DT. You do an extra 326 damage with Hollow Point rounds than AP rounds with a sneak attack critical to a Deathclaw.

Of course, the weapon needs to have a somewhat high critical hit damage. If the weapon does 10 crit damage then don't bother.

Thank you for your answers, that helps.