First, an evil Undead creature shouldn't be a Player Character Race at all. Second, it's Undead (Augmented Magical Beast) as the correct subtype.

Augmented Subtype: creature receives this subtype whenever something happens to change its original type. Some creatures (those with an inherited template) are born with this subtype; others acquire it when they take on an acquired template. The augmented subtype is always paired with the creature’s original type. A creature with the augmented subtype usually has the traits of its current type, but the features of its original type.
Since we don't have the stats for a living grabbit, it's pretty hard to judge what an Undead grabbit should be.

I don't understand Taste of Blood. This makes it sound like something it would get if it successfully bites someone. What is the normal damage a bite does (since this adds extra damage, you need a base damage.

Speed doesn't make a lot of sense. Small creature's usually have a base speed of 20 feet. A fast speed for a Small creature is 30 ft. (40 ft. just strikes me as too fast). If they are so fast, why do they "lurk" and not just chase down their prey. Your text and stats contradict.

Why does this creature have better than average stats? It gets these adjustments just for being Small-- +1 Size, which applies to Armor Class and Attack Bonus, -4 Grapple, and +4 to Hide. I can see giving it +4 Dex but not +2 Str. These are quick opponents not ones that overpower their enemies. I recommend +4 Dex and -2 Str.

A grebblit that has done damage to a creature can take a swift action to taste its blood, or savor a chunk of its flesh.
Since this has the Augmented Magical Beast subtype, it is only proficient with natural attacks. This seems like it has just a bite attack. It is Small, so a Small creature's bite is likely its only attack doing 1d4 damage plus 1 and 1/2 Str damage. It sounds like you just didn't want to call it Rend.

Giving it additional damage equal to 1/2 it's HD scales but I'm not a fan of it. It's a lot easier if it adds a static amount of damage.

I do not understand the "frenzied state" It's a rip-off of Rage but without the cool benefits. The extra damage does not off-set the loss of AC. And that AC penalty is way too severe. I'd never play one of these for that alone.

Blood Hunt is not the best name. Really this is like Bloodsense but with the ooky mist that follows the target. Can everyone see this mist or just the grabbit? How do you get rid of the mist effect? There should be a save to avoid it as well.

They are not born, they are made. They are created by the same All Evil the Melbred serve, created as a wicked accomplice in the consumption of the living.
How, then, are these not Constructs rather than Undead? Again, there is a disconnect between the text and the creature's traits.

Overall, this needs a lot of work to just make sense and be something people want to play rather than be just another adversary to defeat.

Debby