Not sure of the ? If you are asking if an arm laceration would disqualify you from the military than i would say it all depends on the kind of laceration, if underlying tissue is damaged. Evan then if the tissue is repaired it may not be enough to disqualify someone.
Impaired function? Having a significant scar on your arm will not prevent you from becoming enlisted or commissioned. However, if you have significant functional impairment - that will.
Disqualify? I am guessing you mean would such a laceration prevent your entry into the military? If you have any type of injury and the result has been healing with full restoration of function, the military will ignore that in its decision to otherwise qualify you for entry.