I love cocoaDialog, but it seems that Mavericks and Yosemite don't as much. It was always going to be a risk, relying on software that's been stagnating for 2 years without an update... if I had the smarts I'd pick it up, but I don't.
Until someone can take cocoaDialog and update it for Mavericks new security features... (as stated by Greg Neagle - apps need to do very specific things to be allowed to play outside of a logged in user session in 10.9+) ... I've shoehorned a workaround, which whilst not terribly elegant, it does the job.
Patchoo 0.9931 - https://github.com/patchoo/patchoo
It performs a fauxLogout by quitting all apps (this will break [x] Reopen on Login), then uses the ARD framework's LockScreen to prevent user interaction. It also tweaks cocoaDialog LSUIEelement and LSUIPresentation mode for the install run. This hides the Dock and Menu bar. Taddaa!
A kludgey pretty awful, but functional way to lock down whilst we perform software installations.
Grab the latest code and let me know how you go!