I wonder if there's an infestation of worms - causing the vomit?
Vaseline - personally, I wouldn't give my cat vaseline - although it does seem to be a remedy supported by many.
Here's an interesting excerpt from an article: http://www.suite101.com/content/prev...in-cats-a72301
|Both mineral oil and Vaseline are effective hairball remedies, but they should be used with caution. Many owners give their cats mineral oil by mouth as a hairball remedy, but this can have deadly consequences. Cats may accidentally inhale the mineral oil, which can lead to death. A teaspoon of mineral oil can be added to an adult cat's food once or twice a week but should never be force-fed.
Vaseline (also known as petroleum jelly) is safer, and many cats will eat it voluntarily. However, both mineral oil and Vaseline interfere with the absorption of fat-soluble vitamins, which can lead to serious deficiencies if used regularly on a long-term basis, though they should cause no problems if used occasionally or for a short time. Half a teaspoon of Vaseline once or twice a week should be sufficient to treat hairballs. If the cat won't eat it voluntarily, it can be rubbed onto his paws so that he will lick it off.
I think the problem with inhalation of either of these two remedies could be deadly, IMO.
(Not good for humans to inhale, either.
Feeding wet food, (canned food) is very helpful, too - dry food contains only 7-10% of water, where canned food has closer to 78% of water. Some professionals say that the cat may be drinking a lot of water, but that, on dry, the cat consumes only 1/2 the amount of water they need for good health.
I've found, from experience, that as long as I'm feeding 95% wet (canned) food that I have no problems with hairballs.