Interesting problem. I haven't researched this exhaustively or anything, but I'm gonna give an educated guess that you won't be able to find out the device name without the involvement of an agent/client app running on each device. There's several companies out there that do make software for mobile device management, e.g.
http://www.odysseysoftware.com/. Might be worth checking out.
That said, you can probably _find_ the IOS devices on your network by examining characteristics of them. For example, Nmap (
http://nmap.org/) can do OS detection remotely without credentials or anything. It's pretty cool, and I think I've written a blog post or two about how to manipulate Nmap and its data from PowerShell. I can guarantee that it won't give you the device name, though, so I don't know how much work you will want to expend in that direction.
Regarding the web page creation, I can see the value in that. If your wifi AP supports it, you could force clients to redirect to a webpage on connection (thus zero training / device chnages). Then, on the web server, it would be very simple to look at the logs for the HTTP user agent string to determine the type of device. But that won't give you the friendly name of the device.
I'd start by scouring the iTunes app store to see if there are any device management agents that will collect data for you that don't cost an arm and a leg. Maybe they can dump data to a DB--and you can manipulate THAT with PowerShell.