Unfortunately the President can pardon anyone he likes. He can even pardon Hillary Clinton for any crimes she may have committed while serving as Secretary of State, so that she doesn’t have criminal charges hanging over her head during the 2016 presidential campaign.
You are correct that the President can pardon anyone for any crime except treason, and there is nothing to prevent it. However, I am not sure if he can pardon someone for crimes they have not been charged with. For example, I don't know if he could pardon Hillary for any crimes she may have committed during his presidency that might be discovered at a later date...
Because some are saying he has mental issues and was “captive” for five years that any sentencing will be light if at all. However he will loose some of the benefits he has and may loose his military pay.