The simple fact is, there are some analog cameras that are better-suited to specific situations without a corresponding IP counterpart, at least not within a reasonable price range.
Case in point is a regular customer of ours: an upscale restaurant/lounge with fairly low lighting at night, complicated by lots of dark furniture and fixtures, making for some very contrasty situations (halogen pinspots over dark wood tables, etc.).
In all of the last 16-18 sites we've done for them, we've used primarily CNB VCM-24VF "Monalisa" cameras, because for the price point, the Monalisas provide outstanding TDN low-light performance. They're also a very versatile camera, being flush or surface mountable, IP65-rated, with a 2.8-10.5mm lens and a very well designed 3-axis adjustment gimbal. They also have an SBLC (super backlight control) that handles the dynamic range quite well. And most importantly, the customer doesn't hate the dome design too much (the designers would rather have no cameras at all).
Now we're getting in these 2MP/1080p Dahua mini-domes, costing almost exactly the same as the CNBs. They're smaller, lower profile (the designers love them), still a fairly wide view though a fixed lens, and give a really nice picture for the cost... but they're not TDN and frankly, they're lousy in low light. As much as I would have liked to use them instead of the CNBs for this latest site - operations are spread over four floors and being able to go all-network would have made things SO much easier - they just wouldn't be suitable for the dining and lounge areas.
They do, however, work very nicely in the back-of-house areas - office, staff room, lockers, etc - and we've used a number of them for those areas. But for front-of-house, it will be primarily the same CNBs for the foreseeable future.
We HAVE found very good results recently with the Axis P3384 domes and have started using more of those FOH, especially in their new flagship store, but those are about four times the price of the CNBs and minidomes - when you're looking at 30+ cameras per site, that adds up fast.
So in answer to Brian's original question: yes, there can be a benefit to a hybrid system, in certain circumstances. In a school situation, where they're not likely to operate with dimmed lighting, some cheap IP cams may suffice. Then again, if they're wanting to cover things like parking lots and outdoor areas at night, with only street lighting available, they may find it overly expensive to get suitable IP cameras for that task.