A faux hawk hairstyle can easily be brushed back at work so that the employee would still have the option of gelling up after work.
On the other hand, I would not pick this fight with a good employee. Our hairstyles are a big part of our self-expression and identity. This is especially true for younger people.
So, unless there is a really good reason why the employee should not have the faux hawk I would focus on his positive attributes and leave his hair style to him.
Elinor Robin, "The Relationship Mediator," has more than 18 years of experience in mediation while working within the public and private sectors.