I heard that truckers are not allowed to carry a concealed carry weapon because it is against federal regulations. Is this true?
Yes.
WRONG
In the US, there is no federal reg that prohibits truck driver's, engaged in interstate commerce, from carrying/transporting a firearm.
Some states will not honor your carry permit and some states will not allow you to get a permit that they will honor, but you are not prohibited from having them in your truck. The "reg" is largley pushed as a company policy, because the company doesn't want the liability. It is NOT a federal reg/law!