Well, there are all sorts of vector art creation tools in AE. And when you Render to Flash, it goes through an implementation of the Adobe Media Encoder.
From the manual:
While rendering and exporting a movie to a SWF file, After Effects maintains vector graphics as vector objects as much as possible. However, raster images, blending modes, motion blur, some effects, and the contents of nested compositions cannot be represented as vectors in the SWF file and are rasterized.
You can choose to ignore these unsupported items so that the SWF file includes only the After Effects features that can be converted into native SWF elements, or you can choose to rasterize frames that contain unsupported features and add them to the SWF file as JPEG-compressed bitmap images, which may reduce the efficiency of the SWF file.
So see what you can get away with in AE. If it’s just text you oughta be golden.