I am not sure too. However, I kind of remember the booklet says for personnel riding into camp. I am sure there is no harm asking!
Anyway I took my Defensive Riding in July 12 from SSDC. As what @Maja said, I was given a booklet by my CQ or sort. in the booklet, there is this form, which allows you to go SSDC to book the DR without paying. After you passed, bring back the certificate, you will be issued a sticker to paste on ur 11b to certify you are DF cleared!