As far as I know you should get auto operation with the 430EX on a Pro 1. The flash shoe on the Pro 1 has all 5 contacts that the Speedlite needs to communicate with the camera. I don't know if you'll get auto operation in all modes, but in Aperture priority (and probably Program) it should be fine.
I don't know if the auto zoom feature will function. I see no reason why it shouldn't, but since I've nevertried it myself I can't say for sure. If it concerns you a lot, I'd call Cannon and ask. Their customer service line is pretty good. You can reach them toll-free at 800-828-4040.
The 430EX is a good choice, though you might want to go for the new
430EX II. I wouldn't pass up a good deal on the 430EX, but the EX II is worth paying a few more dollars for if you ever intend to use it with a DSLR. It also has a stronger (metal) mounting foot. If you just want something very siimple, there's the
220EX and there's also the new
270EX. I think the 430EX II is worth the extra though. You have full tilt and swivel with the head, plus lots of manual control over exposure and zooming if you want it. It can also be used as a wireless slave if you ever need that capability in a multi-speedlite system.