You can't make an AI that can work out the perfect build spots reletive to there position. NO RTS game does that. They just build a circular/square base and continue going outwards as much as they can (Within some limits).
YES I CAAAAN!!!!
No, seriously, other RTSes might not provide this info... But you have a point here, and there is the "ValidHex" function which returns if the section is bordering, if its valid or invalid, so probably using it its possible for this case, non-valid hexes will be removed from the radius, etc.
I've readed the game's rules, and I can assure you that a unit does get slowed down with grass, it has no pathfinding with that thing, but still the difference is only a little compared to normal terrain, so you might not like to consider that (tough little details make the whole more perfect), and I think its important for CoveringAI, since a unit gets IMPORTANT COVER when the grass is tall enough... Still, we can go through the pain of creating (as I have written before) areas for each thing instead of using a proper function, with every map... ... Which in my opinion it dosen't help with the time we have to mod. Having these functions will indeed save A LOT OF TIME, with things that don't only regard pathfinding, but to other things as well.
In the Flags map, for instance, an AI which uses good reasoning won't send its soldiers on foot to get through the waters in the middle bottom sector if there is an enemy there, and a way to check it quickly is to have a function that gets information about the next hexes, based in the units' trajectory... Oh yeah, no game uses that... But its useful!
About the recon thing, we can check if the tall hexes have enemy units nearby, its not that hard, a recon is like a fast spy, it goes nearby, but instead of hacking something, it gathers information...
The idea of adaptable AI is also to don't have to create 100000 areas in every map. Give it a try.