This varies by state. Google "server wage" and your blood will boil. It's illegal in WA, though — servers make standard minimum wage and employers can't take servers' tips.
Having seen the wrong people get rewarded bonuses, RSUs and raises all the time. You are just better off with a salary band/pay grade and give money uniformly across the band.
Ideally 'top performers' are supposed to be rewarded for 'top performance'. But in any subjective evaluation you are just dealing with cooked up documentation to prove a person did something, therefore deserves extra. Pretty much any and anyone's story can be twisted and narrated in a way that could sound positive or negative, to reward or punish respectively.
You are better off with a tip pool and paying it across the band.
https://www.fordfoundation.org/ideas/equals-change-blog/post...
You're describing "server wage" laws, in which employers are free to steal tips up to the difference between real minimum wage and server wage per hour. In effect, servers in these states make above minimum wage during peak times and at most minimum wage off-peak. But they have to work off-peak or they don't get scheduled for peak hours.
In WA, this form of wage theft is illegal. Your statement, "minimum wage for servers is lower than for untipped workers" is false in Washington state, which is where the wage theft in TFA took place.
I never claimed "server wage" laws apply to this situation.
Also, the term "wage theft" seems like it doesn't apply to "server wage", because "server wage" is a construct specifically created by the law, whereas wage theft is something that's illegal.