Apparently there's a story to it: His wife died from thyroid cancer, and he took solace in WWE events. Somebody in WWE found out about it somehow (I'd guess a wrestler ripped up his sign or something, they brought him backstage to make amends/avoid lawsuits, and that's when they found out, but I don't know for sure) and they basically agreed to give him front-row seats any time he wanted them (hence why he's always in the front row). He pays his own travel expenses, as well as buying new hats (the wrestlers apparently like to wipe their asses/balls on the hats and then put it back on his head), so he's not exactly an employee.
If I remember right, I think it was the Undertaker who ripped up his sign a number of years ago. Taker still had his gut at the time and "sign guy" was in the front row holding up a "Taker's Pregnant" sign. Taker snatched it out of his hands and ripped it up.
I don't know if that's the reason he was brought backstage, though.