Here’s FIBA’s press release on the matter.
If an NBA player requests to play for a club of a FIBA affiliated league, the NBA will not object but will state that the player will have to return to his NBA team as soon as the lockout ends. Consequently, FIBA will deliver a letter of clearance subject to the receipt of a declaration signed by the player, stating that he will return to his NBA team when the lockout is over.
This is a different approach than in 1999, when a number of players, including Nick Van Exel and Reggie Slater, were blocked from going overseas by the NBA and FIBA. Several NBA players, including Deron Williams, have signed with teams abroad, and many others have flirted with the notion. This may encourage more to do so, though time is short since European training camps open soon.