Josh Green has some strong evidence he is:

Gauging the effect of Trump's presidential run on his viewership is a fairly tricky science. There are actually two distinct "Apprentice" shows -- the ordinary "Apprentice" and "Celebrity Apprentice," which is the one currently airing Sunday nights on NBC. What's more, the neither "Apprentice" series runs for a full television season. According to media experts like Feltus, in order to properly measure Trump's effect on his audience it is necessary to do an apples-to-apples comparison -- that is, to measure the current season of "Celebrity Apprentice" against the most recent season of that same show, which aired last spring. (Last fall, NBC also aired a run of the ordinary "Apprentice.")
By that measure, Trump's ratings have clearly dropped. The fall-off has been especially pronounced over the last few weeks, a period that coincides with Trump's emphasis on Obama's birth certificate. "Something is definitely going on there," another media buyer told me. "He's dropped -- and that's a big fucking dip." Given the liberal skew of Trump's viewership, that dip might not be surprising.

So maybe he really is running for president. One GOP pollster he's contacted certainly thinks he is. Who knows. I'm not sure normal logical considerations like "he's doing X in order to achieve Y" apply when you're dealing with that level of megalomania.