If you are satisfied with a "brute force" technique that does not involve disabling System Integrity Protection, and don't mind having three "dividers" in your dock (in place of the Apple SPAM apps), you can replace their "Contents" with the "Contents" of a bare-bones app that does nothing (so much so, in fact, that it is called "Nothing.app" and it does nothing except to launch, quit, and serve as a divider in the dock).
I created "Nothing.app" by starting a new project in Xcode, giving it an icon reminiscent of an earlier generation of the Mac OS X Dock Divider (one that looks a bit like crosswalk stripes), then stripping out everything except the menus "About Nothing" and "Quit."
You can download a zip file containing "Nothing.app" here: https://www.dropbox.com/s/6lb8m35nufnd1mz/Nothing.app.zip?dl=0
If you're uncomfortable downloading an app from a stranger, you can stop here. Otherwise, you can examine the contents of the app and see that it is just the husk of an app.
- In the dock, right-click any Apple SPAM app you want to eliminate (say, "iBooks") and choose Options > Reveal in Finder.
- Right-click iBooks and choose "Duplicate" to keep an unmodified copy in case you actually want to use it at some point in the future. This copy will not be kept up to date by the App Store.
- Right-click the original iBooks again and choose "Show Package Contents"
- In another finder window, right-click Nothing.app and choose "Show Package Contents"
- Drag the "Contents" folder from "Nothing.app" into the "iBooks.app" folder.
- Choose "Replace" (you will be prompted to authenticate yourself, as Apple's SPAM apps are protected against casual modification).
- In the dock, double-click iBooks
- The "Nothing" app will launch, and the iBooks icon will change to a divider.
- Drag the divider anywhere in the dock that you want it.
- Repeat with Photos and Maps, if desired.
PS: I have not had this in place through an update from Apple of any of the SPAM apps: it is possible that this change will be replaced when the app is updated, so keep a copy of Nothing.app handy to redo the "Contents" replacement, if desired.