If something as obvious and simple as CoO can easily counter the invisible fruit, then there is no point in giving it to him. Zoro can already follow invisible shit, which he proved against Kaido. Also, Sanji couldn't detect Queen with CoO. So if a second-class ability that doesn't really make you invisible can bypass CoO, then there is a high chance a strong character with the original ability would be able to do it too.
And the reason why he's given this fruit is probably that being stealthy was the most highlighted aspect about Shiryu when he was first introduced. If you remember it, he was moving around in ID without being detected or seen by the surveillance team.
