I have no relation to dropbox other than using it. My guess would be that it is a requirement if the person applying chooses to make it a requirement.
To me it's a question of reality. Within any interaction each person has a different version of reality. In order to interact, the participants have to agree on a common version of reality.
In this case - The applicant's reality should be that it is not a requirement. The company's reality is that it is a requirement. If the applicant can convince the company that the applicant's reality is the right one to use for the common ground, then the requirement is not a requirement.
To me it's a question of reality. Within any interaction each person has a different version of reality. In order to interact, the participants have to agree on a common version of reality.
In this case - The applicant's reality should be that it is not a requirement. The company's reality is that it is a requirement. If the applicant can convince the company that the applicant's reality is the right one to use for the common ground, then the requirement is not a requirement.