i used to be a vendor that worked exclusively in walmart for 8.5 years (till the economy went in the tank) about 4 or 5 years ago WM got rid of most of their LP folks in the stores (larger stores used to have 4 or so folks that walked the store and someone in the video room) most all super centers have 1 LP person on staff that mainly stays in the video room and works 8-5 with some weekends and some nights and a few overnights
as far as the cameras go they all automatically record to a hard drive (used to be VHS) and the majority of the time they are looking for employee theft
as far as the video room the LP, store management, and above (market, regional, ect) are allowed in the room when it is in a separate special room (it is in nearly every super center) but in some old stores (esp regular, non grocery, stores) the monitors and recording equipment is located in the managers office
as far as finding customers who are stealing mainly that is left to employees working on the floor and if they really want to have LP or management observe someone they will use walkies or page with codes (such as "Mr/Mrs X you have a call on line Y", where as X is a made up codename for LP in the store and line Y is what section that needs to looked at) when you here them announce "security cameras please scan and record section Y" that is just a ruse used to keep people honest
just some trivia for ya'll about walmart LP (it's amazing what you pick up when you work in WM for 8.5 years and work with all levels of management and supply chain and LP)