Home Depot employees here in Canada are already doing something similar, and I confirmed with management - when I complained about the behaviour - that it's an edict from on high. The practice drives me right fucking crazy. It has, on several occasions, caused me to go far out of my way to a Rona store where they don't do that.
When I'm in such a store, I'm in one of two modes. Most often I'm problem solving, looking for some thing or things yet-unknown that represent a solution. In that case I'm thinking, and your "Hello" breaks my train of thought. Other times, I know what I want; if I know where it is get out of my way, and if I don't know then I'll find YOU and ask for your help.
It's downright creepy the way they insist on saying "hello" while walking toward me, when I'm very obviously giving them as wide a berth as possible while deliberately and clearly not making eye contact. If I'm not meeting your gaze, don't talk to me - we're not buds, we have no relationship outside of this store, and you're invading my personal space and interrupting my thoughts. Simple rule: treat me as though we're walking in opposite directions on the sidewalk. If we mutually make eye contact, say hello. If we don't, keep your silence. This isn't a bar or a party - I'm here on business and if I need your help you'll definitely know because I'll ask for it.
I've heard about stores in Japan that have two colours of shopping baskets; one signals that the customer is willing to be approached by an employee, and the other says "don't call me, I'll call you". This strikes me as a perfect solution. But I suspect that it's far too sensible - and too far counter to the smug rapaciousness of the North American business mentality - to ever be adopted here.