The employer can place whatever requirements for employment they like.
Sorry, but if the employment requirements break the law, the fact that those requirements are laid out in a contract doesn't matter at all.
In California, which is where Diskeeper is based, state law says the following:
(a) For an employer, because of the race, religious creed, color,
national origin, ancestry, physical disability, mental disability,
medical condition, marital status, sex, age, or sexual orientation of
any person, to refuse to hire or employ the person or to refuse to
select the person for a training program leading to employment, or to
bar or to discharge the person from employment or from a training
program leading to employment, or to discriminate against the person
in compensation or in terms, conditions, or privileges of employment.
Forcing you to go to CoS classes as part of your terms of employment certainly seems at first glance to run afoul of California's FEHA at the very least, if not Federal law as well.