You need to check with a Senior Careers Advisor who can give you a definitive answer. The basic qualification is 5 GCSEs at grade A-C including English language, maths and a science or foreign language; 240 UCAS points (i.e., the equivalent of 2 A levels at grade A) or their equivalents from Scotland and/or any similarly barbarous location from which we accept officer cadets. Equivalency is tricky and I believe it's the senior education advisor at AOSB who makes the final call, but an SCA should be able to get access to some proper advice in your case.
No it doesn't count. You cannot say what it equates too (maths etc). There is no test at the end of the course and it does not confirm any academic ability. Colleges make a massive thing of 'it equates to this and you can join the Army as an officer after this course. It does NOT equate, you just gain the same number of points. You cannot join as an officer on this course alone.
Just to slightly amendment to cpunk's relply - Itis a minimum of ALIS points from you top 7 GCSE's, not 5. You must have completed all 7 GCSE's. Three of the subjects must be those he highlighted.