Swallow tails are supposed to handle steep drops very well. Each tail acts as a pin tail when you're dropping in on an angle. once in the wave it should turn a bit looser than the round pin.
Thats not to say that a wide flat-rockered fish is going to be easy to handle in those conditions - it won't be. but swallow tailed shortboard is fine - probably easier to make the drops than a squash.
swallow tail should allow you turn quicker. I ride a squash tail in anything over head high though and my swallow tail when its smaller. I am more concerned with rocker and length when the waves start getting bigger and faster. My swallow tail has a low entry rocker which means its better when its smaller, 6 ft or under. I have more rocker on my standard shortboard which happens to be a squash.