As far as I know, you can use DirectX and OpenGL in the same program, and allow the user to select which he prefers.  You might even be able to use them at the same time, but that seems like a bad idea.

It's an interesting game concept.  Here are some ideas that I came up with while reading it, I hope you don't mind.

While in a nation vs. nation battle, the bots that are fighting for absent players should each represent the player it's standing in for.  The bot should have all the abilities of the player, but be controlled by the server/guildmaster/commander.  What happens to that bot should also happen to that player, such as any penalties and possibly stat increases/level ups.  You would need to be careful while designing that though, since it could make "auto-leveling" easier.

It would be cool if the guildmaster/command can directly control the bots like in an RTS game.  But since the bots are representing another player, they should have some chance of disobeying orders.  Perhaps the guildmaster/commander and all the players and bots have a loyalty score.  Having a high loyalty score as a guildmaster/commander would show players that your commands are trustworthy, and give a number to roll against for bots.  In the case of players, their loyalty score is used if a bot needs to stand in for them.  If the player has a low loyalty score, the bot that represents him will be less likely to follow an order, even if the guildmaster/commander has a high loyalty score.

Loyalty for the guildmaster/command could increase by winning a battle.  It could also increase by issuing an order that, if followed, doesn't get the players/bots involved killed.  A player/bot's loyalty score could increase by following an order, and increase even further if that player/bot succeeds at whatever the order was.  The opposite would decrease the loyalty score.  Losing a battle or getting their soldiers killed while following an order would decrease the guildmaster/commander's loyalty score.  Not following an order or not succeeding in a mission (order from a guildmaster/commander) would decrease a player/bot's loyalty score.

The team at IfThen Software LLC has been working on an MMORPG under the code name "Loradon 3.0". It's been in production for a couple of years already and we are planning to release a preview soon.

Website: http://www.ifthensoftware.net/loradon_online/
Forums: http://www.ifthensoftware.net/forums/
Screenshots

To show our current progress, the development team has setup a couple Twitter accounts. Twitter is like a quick, mini-blog. The lead programmer and the lead artist both have Twitter accounts and update them as they work on the game. The Loradon 3.0 website has a widget on the main page that shows both Twitters at the same time. You can also visit each Twitter page directly by clicking on the following links:

Lead Programmer - InvisibleMan
http://www.twitter.com/ITS_Invisible

Lead Artist - GreyKnight
http://www.twitter.com/ITS_GreyKnight