My guess is that Linderman is not really Linderman at all. We think it's Linderman because of his healing powers, but in season 1, Linderman specifically said that, dispite his powers, he couldn't bring someone back from the dead and Nathan was pronouced dead on the operating table. Also, Linderman never had the power to selectively make certain people unable to see him. And third, D.L. clearly killed him. Even if Adam had a chance to revive him after he escaped, Linderman had already been dead and buried for four months.
No, I think that "Linderman" is actually Arthur Petrelli. How? Because I think Arthur Petrelli, like his son Peter, can also copy other peoples powers and so he has the powers of all the founding members, including Linderman, Adam, and, more importantly, Parkman's dad, who has advanced telepathy to not only read minds but to plant suggestions into others--like making a person think they are seeing someone else or making themselves invisible to others, for instance. Which would be a perfect explanation as to why only Nathan can see "Linderman" and how "Linderman" instantly knew that Tracy was not Niki. And it would explain how Nathan was healed because he used the "healing blood" technique.