I think the monster found Zampano because he was researching the house, as that's the monster's primary residence it seems. It zeros in on people the more they know/find out about the house. Taking the alliteration that the monster is the minotaur, as Johnny's dreams suggest, than my theory is that it has to work it's way into your mind before it finds you. Remember the old saying, "The eyes are a window to a man's soul?" that's how it does it--you read about the house, you open the proverbial window to let it in.

As far as the whole 'Zampano is Navidson' thing, I'm not so sure. After reading the The Whalestone Letters there's more evidence that Zampano and Pelafina knew or corresponded with one another. And In that case, the time frames don't match. Pelafina was at The Whale from 1982 to 1989 and unless the 'My dear Zampano, who have you lost?' question refers to Delial, it just doesn't make sense. And yes, I know Pelafina was nuts and prone to not making sense, but I have another theory that might take a little explaining:
Pelafina is Zampano, or rather, created Zampano.
I offer this quote from the foreward of The Whalestone Letters:

"I was suddenly infused by the sharp sense I had experienced only once before, though also in her presence, and one gratefully the direcetor confessed to having also sustained: somehow she managed to make you feel as if she had invented you."

My theory going on that is that Pelafina had contact with Zampano, and The All that Pelafina rants about is the House. That's just how Zampano interpreted it, and he was so fasinated by the concept that he willed it into being. The House, Navidson, it all sprung from Pelafina and was transformed from madness to lucidity by Zampano--problem is it drove him nuts.

This could be a strong argument for the unreality of the House, but I think not. It's been proven that skitzophrenics like Pelafina use a hell of a lot more of their brain than neurologists even know what it's for, so in this case, I'm taking the phrase 'willed into being' literally. Pelafina constantly makes the point to Johnny that words are the only real thing in the world. Her words, filtered through Zampano created the House and everything associated with it, which explains why no one Johnny talks to knows what the hell he's raving about. Because the House only truely existed for the time that Pelafina and Zampano were alive. Both were dead by the time Johnny starts looking into the House.

Out there, I know, but neat to ponder.

__________________
"You may call me whatever you wish, but I'm taking your cake."
~ 'L'