Generally this would not work unless one the merchant already has Bitcoin on hand, and two, the employees actually want payment in Bitcoins. Also 1 USD stays fairly close to 1 USD over a 2 week pay period or even on a yearly basis. Bitcoin, right now, fluctuates so much in price, someone's pay could be greatly effected by the current price of Bitcoin.
If a merchant already has cash on hand, it doesn't cost him anything to pay their employees. Not including any fees for a payroll provider, HR manager, etc.