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.
OpenRA's bots are a bit more clever, and also don't need to magically see into fog-of-war.