我认为这样的表达是可以的。在词典上一时间很难查到此类搭配，但英美人在相互交流中常这样说，因此我查了美国当代英语语料库（COCA），结果发现很多这样的例句：
She can just live happy and free.
And you'll live happy among your own people.
I want to live happy, because we don't live forever.
I wake up happy in the morning, that is why I want to live happy later on in my life.
And is there a solution for you to live happy and to live in this matrix(society)?
May all peoples and folk live happy and self-determined in a friendship of sovereign nations.
分析如下：
They live happy. = They are happy when they live.
They live happily. = They live in a happy way.
也就是说，happy说明主语“They”，是“主语补足语”；happily修饰动词“live”，是“方式状语”。再比较两组句子：
The plane landed safe. = The plane was safe when it landed.
The plane landed safely. = The plane landed in a safe way.
He sat quiet on a chair. = He was quiet when he sat on a chair.
He sat quietly on a chair. = He sat on a chair in a quiet way.
