My friend told me that a Schutzhund dog that has been trained to bite a sleeve can never be a Personal Protection dog because it will not bite a person. Is this true?

I recommend that your friend get more experience and stop passing along bad information like this.

It is true that a lot of Schutzhund dogs can never do personal protection work because they are only trained in prey drive and or they simply do not have the nerves for the work.

With this said, many dogs have the correct character to do both Schutzhund and personal protection. Dogs that do have the right nerve and drives will need additional training to do personal protection work. For those who are just starting to learn about protection training - Schutzhund is a dog sport it's not personal protection training.