The following implies that it might be possible.
Unified Editor Sweet multiplatform development has come of age! As of Unity 3 one editor targets all platforms. Want to make a game for iPhone, web and XBox 360? No problem. Have everything you need in one project and simply choose which platform you're currently previewing inside the editor to see exactly how your game works
Unity iPhone produces an XCode project, and XCode only runs on OS X. You could probably create iPhone apps on Windows but you wouldn't be able to make any builds.
No. Apple has made it crystal clear in their developer license agreement that you may not develop an iphone/ipad game on anything other than the Mac operating system. As far as I know, there would be no technical limitation preventing Unity from supporting that, but the legal restrictions do.
You can create a game in unity on windows, then transfer the project to a mac when its time to port to the ipad/iphone. Just to be clear, though, ever iphone app/game development tool requires you to first buy an apple developer license and that license requires you to only develop on an "Intel-based Mac running Mac OS X Snow Leopard or later".
In the end if you plan on selling your app on iTunes - YOU WILL need to compile with your certificate and code-sign your project in the build setting of xcode. You will need an authorization certificate from Apple (including a separate one if you include push) No way around this you will need a Mac. They have tools that can tell if you used xcode that run ahead of the approval process to weed out applications.
If you are going to build an application for a platform you need to adopt the platform and embrace it.