Simple answer? Yes. In Naval Architecture-speak, this is called the "point of vanishing stability." However, when sailing such a small boat, you can modify that point considerably. I can get my boat to about 50-60 degrees without capsizing.
The point of vanishing stability for a cruise ship, for example, is pretty well fixed. The weight of the passengers and their effects, while not insignificant, is much less than the weight of the ship's structure, machinery, outfitting, fuel, ballast, stores, etc. When it reaches the point of vanishing stability, it will roll and continue to roll until it finds a more stable point - usually either on it's side or upside down. However, one of the key factors in the point of vanishing stability is the "center of gravity," or center of weight, both it's height and transverse position. On a Hobie cat, the weight of the crew makes up nearly half of the total loaded weight of the boat. Moving your weight further outboard and down lower effectively increases stability of the boat and increases the "righting moment," or the "force" trying to keep the boat upright. There is also a "heeling moment," which is essentially the "force" trying to heel or capsize the boat - caused by the lift in your sails and rudders. This too can be modified by letting your sheets out, pinching higher into the wind, or "turning down" to use the lift on your rudder to counteract the heeling moment. Once capsized, the next stable point is on it's side, unless you have a leaky mast, in which case it's upside down.
The point in all of this is that two of the primary factors in determining the point of vanishing stability are very much in your control and can be drastically altered to keep from capsizing. Imagine if you were sitting on the leeward side of the boat when a gust hit - the boat will go over a lot faster and capsize a lot sooner than if you were out on the wire, and let the mainsheet out in a puff. That said, there will always be a point where you've exhausted your options to keep the boat upright and it will capsize.
Capsizing on a Hobie cat is nothing to fear, however. It's not as violent and doesn't happen anywhere near as quickly as it sounds. After about 45 degrees, the mast seems to "float" down to the water. As long as you're not completely unprepared for it, it gives you plenty of time to sit up on the side of the boat, grab onto something, and/or jump clear. As long as you have enough weight to right the boat, it's no big deal whatsoever, once you've experienced it. I agree with John; on a moderately windy day, try with a friend to get the boat as high in the air as you can without capsizing (it's exhilerating!). When you inevitably do capsize, don't panic, just hold on until the boat is on it's side, then jump clear. Read up on righting technique and watch some youtube videos so you know how to do it, then give it a shot! You'll be amazed at how simple it is!
'79 H18 standard 'Rocketman II
' sail #14921