Belo Plan: Employer controlling hours worked?

I work for a company that has been using a Belo plan for a few years. In researching more about the requirements for a Belo plan, I have come across: "the nature of the employee's duties must be such that neither he nor his employer can either control or anticipate with any degree of certainty the number of hours he must work from week to week." [29 CFR 778.405] How much control/certainty can the employer have over hours worked per week and this criteria still be met for a Belo agreement?

There are 2 parts to the employees' work week: There are the off-site duties that are determined by the client, and there are on-site duties of equipment maintenance and general warehouse work. The warehouse work is the part of the employees' duties that is controlled by the employer. The employer schedules the warehouse hours based on how much time the employees have spent off-site that week. However, the nature of this industry has the employees working in excess of 100 hour weeks for a few weeks out of the year. The rest of the time the employer has the ability to (and does) balance out how many hours the employees work in a week by fluctuating warehouse hours based on time spent off-site that week.
Is this situation abiding by the legal restrictions of a Belo agreement?