I don't think you'll find any University that officially has any interest with PHP - PHP has a lot of problems with it that make it far from ideal for teaching programming theory, it's object-orientated interface and a backwards view of variable scope to name just two.
That said, I'm sure some universities will run modules in web-based technologies and I would think PHP would feature there due to it's ease-of-use and how widespread it is. Also, I would say a lot of students would pick it up for personal use (I learnt PHP while I was at uni, but it wasn't even mentioned as part of my Comp. Sci. degree, for instance.) Therefore you'll likely find a lot of interest for such contests.
May I make the suggestion though that you run contests that any team can enter, and have special awards for student entries - This will make the contests more interesting for all due to the increased participation, and the students would still get the recognition they deserve by entering.
Of course, you might find everything I've wrote is not true, and many unis are offering modules specifically teaching PHP
Regards,
Carl.