是的，it 是形式主语，that 从句为真正的主语。比较：

It is likely that he will win.

= That he will win is likely.

又如：

It’s very likely that she’ll ring me tonight. 很可能今晚她给我打电话。

=That she’ll ring me tonight is very likely. 很可能今晚她给我打电话。

It is likely that the factory will have to close. 这家工厂可能要关闭。

= That the factory will have to close is likely. 这家工厂可能要关闭。