O'Brien has given his first interview since the Irish squad was announced. Although Kent didn't technically refuse to release him, they made it clear that he might not get his place back after the tournament. Sounds a little like blackmail to me, not that I'm accusing Kent of anything. Kent have released Amjad Khan to play for Denmark though.
Full Interview
The counties have been pretty good at releasing players so far. Here is a full list of players from teams in the ICC Trophy involved in county cricket.
Scotland
Gavin Hamilton (Durham) - released
Kyle Coetzer (Durham) - TBA
John Blain (Yorkshire) - TBA
Dougie Brown (Warwickshire) - released
I assume that if Durham are relasing Hamilton, they'll also release Coetzer. Durham have had pretty good relations with the SCU in recent years.
Ireland
Ed Joyce (Middlesex) - released
Eoin Morgan (Middlesex) - released
Andrew White (Northamptonshire) - released
Niall O'Brien (Kent) - not released
Denmark
Amjad Khan (Kent) - released