Although the exact causes of attention deficit hyperactivity disorder (ADHD) are not entirely known or understood, there is probably a strong genetic component. Definitely ADHD is not contagious and cannot be passed from one child to another. Therefore, on the surface, I don't think you need to worry
Nevertheless, some children with ADHD can have higher rates of impulsivity, anger control, and risky behavior. This can especially be a problem for teenagers, as it may lead toward substance use and other dangerous behaviors.
Therefore, there is no substitute for getting to know your son's friends well. If you are convinced that they are good friends and that there is no danger of getting your son involved in risky behavior then you should be fine.
It is helpful to maintain an open ended approach when asking your son about his friendships. This will let him know that you support him and his choice of friends but also that you are available to talk about anything that bothers him. It is always, as a general rule of parenting, a good idea to set clear expectations about what is and what is not acceptable behavior.
Talk to your pediatrician
if you have more questions!