IIRC the RA1 skirmish mode AIs always had perfect information and resource multipliers based on difficulty. RA2 did it a little differently with "virtual ore purifiers" added for the high difficulty AIs. I'm sure a similar thing was done for the Tiberian Dawn campaign and the Tiberian Sun multiplayer/skirmish AIs.
OpenRA's bots are a bit more clever, and also don't need to magically see into fog-of-war.
I never played much of RA2, but played hundreds of hours of RA1 skirmish. Must have been that. Thanks for the insight!
Skirmish was a blast- I'd turtle until I had the enormous battleships (cruisers?) that could fire onto land. Loads of fun when I was like 12.