That rather depends on the company officials handling the complaint and the policy/procedures of the particular company. Each company is different as is each complaint made. It is not automatic that the company officials would presume the employee "guilty" or require the employee to prove anything. In any event, there are any number of ways that a disgruntled ex-employee might try to get revenge against his/her former supervisor. Indeed, there are several ways the disgruntled employee could make anonymous complaints the company management. This service does not enable the disgruntled employee to do anything that he or she couldn't do some other way.
And anyone could send an anonymous letter to the company management, too. So at least given my understanding of what this service does, I'm not seeing anything particularly special or unique here that would be cause to single it out for particular concern. Is there something you see here that raises a legal issue?

