Can allies really attack allies?

[Dirt road Joe]

The perfect scenario: (only an example)
Pretend that every member of FUN(Forum United Nation) and MoC(Murder of Crows) were allies with each other and had similar stats. So whenever they are doing their daily PVP they wouldn't be able to attack/Raid each other due to being allies.
But what if they were matched up come Conquest time to fight each other due to having similar stats? Since in reality they are all friends within the system, would the war allow them to fight each other and forfeit all alliance? Just a random idea I had come to mind? Would any scenario like this be possible wether it be a whole alliance throughout both guilds or just a few, would the servers allow these kinds of matches to happen.
Just a thought! Let me know what you think.

[Dexter Morgan]

When guilds start you will be able to attack anyone in the guild you are matched up with, whether they are allies or not.