Why in hell would you like to include flash code into pascal application? This would only introduce more problems if for instance end users won't have necessary runtime libraries to run this flash code on their computers. Not to mention the fact that you would be forced to seperately debug pascal and flash based code.

Creation of layouts and animations in OpenGL isn't as hard as it seems.
Example of how to create slidable menu:
1. Render the whole menu to special texture usually refered as RenderTexture.
2. Create Quad with desired dimensions.
3. Render the Menu texture onto the Quad either using scaling (streching efect) or partial rendering (sliding efect).
Verry similar process is used in FireMonkey. But the biggest probem of FireMonkey is that every controll is seperate single texture rendered on a Quad. That's why when you ZoomIn on FM panel the othervise few pixel thich borderline becomes several milimeter thich black line on the screen (verry ugly by my opinion).

As for UI layout it is only up to you how will you make it.

Since most graphic engines nowadays do have support for RenderTextures you can use theese for optimizing the RenderingRoutine. How?
Lets say that you want to have your games UI divided into several sections where each of this sections is actually created from many small componets (pictures). If theese sections doesn't change often it would be more eficient to render seperate sections into RenderTextures and then update this texture only when necessary. So if section is othervise composed from 10 pictures you can save upto 9 "DrawPictureHere" cals when this section hasn't change from last frame.

Many 3D games make use of RenderTextures for rendering dynamic content on ingame Monitors (survalience cameras, computer screens, TV's, bilboards, mirrors, etc).