You will find considerable differences in security policy across the product lines of some manufactures. For example, Optera may show different results than other cameras from that same manufacturer, given the camera's heritage. Not saying it'd be better or worse, but maybe different.
That implies a potential lack of consistency of non-functional attributes like security policy. Which is one thing you want to chase out if we're talking about manufacturers and their reputation for producing secure products. The most secure will be those that take a holistic approach to security across their entire product lines, not just individual products. If tomorrow they slam a cheap OEM camera into the line it could present unexpected risk, unless they're managing those policies across the board.
IT security in video surveillance can be tricky business because the products sometimes straddle the identity between a fully embedded product and that of software based on an open platform like Windows or Linux--this is especially true on the VMS side of course.