Can I use my iPhone as a "remote" for my iPad? iPhones and iPads both have several apps aimed to be remotes for the PC/Mac -- mostly geared towards specific apps.  That's not what I'm asking about.

I'm interested in any way of using my iPad and iPhone/iPod touch side-by-side where the iPhone presents a menu of commands to control the iPad -- things like shortcuts, or better yet, buttons that invoke user-definable macros.

Does it exist?

Does the iPad have any way of being scripted through an API?

Note: VNC is irrelevant to this question.
It's possible to get your actual iPad screen and control it on your iPhone, but the iPad needs to be jailbroken. There's an always up to date guide of how to jailbreak at Lifehacker. 

Once Cydia's been set up, tap Search and enter Veency. Choose the first option, then press Install and Confirm. When it's done, press Restart SpringBoard. 

After the restart, unlock your iPad and go to Settings. A new section called “Extensions” will appear in the list on the left; tap Veency under it.

Turn on the Enabled switch if it isn't already, then enter a password in the box. If you don't enter a password, you will need to accept or decline every request to connect to your iPad. 

Now connect both the iPhone and iPad to the same Wi-Fi network. This is important because your connection will be slow over 3G. 

On the iPad, open the Wi-Fi settings and then the arrow next to your Wi-Fi. Write down the IP address. 

Get your iPhone and download Mocha VNC from the App Store. Open it and set it up for your iPad's IP address and connect. Refer to its help page for more information. 

The free version of Mocha VNC will let you type using the keyboard and tap the screen, but only the paid version will let you scroll up and down. 

When you're done, press the menu button at the bottom of your iPhone's screen, followed by Disconnect. On your iPad, go back to Settings and turn Veency off. This will prevent anyone from using your iPad over VNC without you knowing, as well as save a bit of battery life.