Update:

I've now tested out Milestone's XProtect and Blue Iris, using my Logitech C910 as a test camera.

Both were able to connect to the webcam with little difficulty, and both were able to record using it with no problems. It acted just like any security camera would. I think Blue Iris handled it a little better, as XProtect did a weird thing where it added four cameras, with only the third being my webcam and the others were blank. Strange.

Overall, it's clear that XProtect is a higher end application. You can do multi-camera reviewing (pick a time and when you scrub through it shows what's happening on multiple cameras), and in Blue Iris you can only review one camera at a time. I also don't like that BI (I'll call them XP and BI from now on, it's easier to type) doesn't give you a timeline with indicators on it that show when it saw movement. Instead, it creates a timeline of "Alerts" which are basically just shortcuts to the recorded video of the points where it detected motion. It's a little clunky IMO, but not the end of the world. It's just not as polished as XP.

But despite being clunkier and more challenging, I have to say I'm fine with BI. For $50 I can connect up to 64 cameras (I can't imagine that many would actually work), whereas XP would cost $100 to start with $50/camera after the first two, allowing up to 26 cams. That gets really expensive really fast.

The biggest drawback to BI is a technical one. Apparently BI isn't advanced enough to leave motion detection to the cameras that support on-board motion detection like XP can. This means the motion detection is done by BI its self, which of course means far greater system resources are needed. It's possible that the money I save my family's church by going with BI might be negated by the need for a new computer to actually run the software. I don't know really. I'm going to observe the CPU usage of my own computer, which is considerably more powerful than the one being tasked for this project (uh-oh), and see how much power the program needs. It'll be interesting.