I suspect that most of the dive ops are renting equipment to a large percentage of their clientele. I don't know what percentage, but I bet it's pretty high. So, I imagine it's pretty safe. Most regs are pretty reliable these days, so I wouldn't be too worried about that. It's more of a comfort issue; wetuit fit would be the biggest concern, followed by BC fit, and to a lesser extent, BC design.
Depending on when your trip is, you might check out Christi's thread "exposure..." where she warns about the current jellyfish situation. Many of the dive ops only rent shorties as they are easier to fit a variety of people. If you can afford to get wersuits before you go, I think you'll find that owning your own suit, one that fits well, will make the biggest impact on your diving of any gear.