And by horse, we mean marketing department. From "Dodgers tab players, celebs for newest marketing campaign" by Michael Becker at the Press-Enterprise blog:
The point, said Harlan Hendrickson, the senior director of marketing and consumer development for the Dodgers, is that anyone can be a Dodger fan.
"How can I tell a band like Nickelback you're not a real fan of the Dodgers? You're not a real Dodger fan because you're Canadian? They wear our Dodger stuff on stage. They want to be with us."
Most of the featured celebrities have either thrown out the first pitch at a recent game or expressed a strong desire to lend their image. Only Yoda's participation was negotiated, Hendrickson said. The rest of the deals were done by handshake.
The fact that not all celebrities are well known - or well-liked - plays into the campaign.
"It's participatory," said Dodgers executive vice president Dr. Charles Steinberg. "They debate whether that person merits a billboard."
The article goes on to confirm that this dude is indeed skateboarding legend Tony Alva (Dogtown and Z-Boys: recommended!).
There you have it: Some of the billboard randomness is not quite so random, yet it's intended to be a little random because there are Dodger fans of all stripes. So the next time someone asks you what you and Bret Michaels have in common, you now have an answer.