Bloodhunter's Blood Sense should track invisible heroes as well. It just doesn't make sense for you to know where the enemy is but not see him. Either give Bloodhunter and his allies the sight, or give it to Bloodhunter only.
How does it not make sense? He senses the area he's in, but that doesn't mean you can see him. A dog can smell someone hiding, but doesn't necessarily know where they are.
Then what would be the point of knowing an enemy's location without seeing him? Especially if he's just around you. It's not like most heroes can do much with red health.