Hey Drew,
Unfortunately not. There's no low level method for Keyboard Maestro to detect when you've entered a text field and thus change its behavior.
The best you can do is set your single-key macros up as a palette that can be toggled on/off.
I do this in several apps, and I want the palette visible to give remind me that things are different.
E.g. I want that strong visual cue that 1-key shortcuts are active.
Here's an example:
Hotkeys/macros only activated on one specified (certain) url
-Chris