What about calling Apple and working with them to see if there is an API that can be used?
We use another asset management tool for all our computer and computer peripherals. This other asset tool is required for our job, but it has no Macintosh support. For the Dells we can run a script on the local computers and those computers will get populated with most of the relevant information. We still need to manually key in the warranty info for the Dells, as well as manually entering all the information for other peripherals, (Wacom, printers, monitors, etc.)
I have also had problems looking up the warranty information manually from Apple's site. If I now go to the Apple Warranty lookup page and start entering in computers I can only do about 5 or 6 systems before the page indicates;
"We're Sorry
We're unable to complete your request. Please try again."
I then need to wait for a while before being able to use the warranty lookup again.