Deploying Pages, Keynote and Numbers?

Have you tried to do this with AutoPkgr? I've had nothing but success with that, although it keeps the Apple ID of the user who installed it when installing on other computers. If that works for you, then AutoPkgr may work for you.

See here for information on AutoPkgr

You may want to talk to your Apple SE/Rep regarding deploying the software in that method.
You might need to go the VPP route even if just to account for the licensing legalities.

As for your technical issue. I would install them via a policy rather than a configuration at imaging time. I'm not a fan of Casper Imaging by any stretch and I have always had much greater success with using deployment policies to setup machines. You might have casper imaging run a script at first boot which simply triggers a policy to install iwork/ilife for example

Any errors during imaging? Check /var/log/jamf.log and look for the iWorks installers and see if they are throwing up anything out of the ordinary.

Going with the VPP route after talking with some people.

I'm curious of the legalities on this in regards to numbers, pages and keynote. All of these are made available for free on new macs, if all my macs are new and are new enough to be entitled to install them I'm curious how this works for an imaged mac.

@jasontucker So when I've talked to our SE the official stance is you should use VPP managed distribution. The grey stance is Apple is well aware that packaging and deploying the apps occurs but you should have enough licenses to cover your deployments. Technically the license doesn't follow the machine, but the first time user of a macintosh has the opportunity to claim a "free" license of the requisite software. I did the thing a while back to get the free managed distribution licenses for purchased macs. It was a bit of a hassle since I don't directly deal with purchasing but our rep was able to get it all sorted out and I supplied the iTunes store address with a list of serial numbers and I was granted the requisite licenses.

Short of it, you should file for your managed distribution licenses, ensure you have license to cover your deployments, and you may deploy as you see fit.

I do disable the ability to claim the free license via config profile as dictated by our legal department.

Relevant support articles:

Volume Purchase Program: Requesting free iLife and iWork apps for Mac
Request free iLife and iWork apps for iOS through the Volume Purchase Program

Going VPP, as you've seen is the most agreeable way with Apple. What I find interesting is that we run a BYOD program, and have to maintain students licenses for those titles as they will need to leave with their relevant licensing. Yet we must ensure that they all use the exact same version of these titles for compatability reasons. Because of this we feel comfortable with creating receiptless packages that require the students to authenticate with their AppleID for continued legal updates, while maintaining version uniformity.

I'm going the VPP route and requested the free iWork apps for Mac, however it seems that these apps will only install onto the latest OS, in this case 10.11 El Capitan. Is that how this works?

If you are going the VPP route, has anyone run into issues with not being able to locate invoices for machines? My company has around 75 MacBooks (pro and air) and since we are a merged company our documentation for all of the machines is not easily accessible, will this prevent me from being able to obtain the free iWork apps? If so, any relatively easy workarounds?