Well they could give you the extra points, but the name of the game is weight loss, and losing that bit of blood doesn't help with the weight loss.
Now you mentioned both - did you give blood or plasma? I've been in plasma banking for 18 years so I might be able to help. If you give plasma, you only need to eat a regular balanced breakfast like you normally would. And when you leave, you should feel like you did when you come in, as long as they give you saline. Most plasma centers do give saline. Plasma is mostly water. You just need to eat a balanced diet and stay hydrated and your body will make the plasma just fine.
Another option for you is to donate between a meal and a snacktime. Bring your meal or snack, and when you are through with your donation, have your own planned meal/snack that you brought along. As long as you have something reasonably healthy they will probably be ok with it. The juice and cookies don't do anything for building your plasma back up. The fluid is to replace fluid you lost, and the cookies/crackers are to make you feel a little more stabilized. We have a diet controlled diabetic donor that donates in my town and she brings a sandwich and a drink with her and as soon as her donation is over, she goes to the lobby and has her sandwich before she leaves. This way she gets the balance she needs. I bet your blood center would work with you also.
Now with alll that aside, I think this is a great tool for you to learn to keep the weight off after you lose it! Your body isn't going to lose weight or maintain a loss if you don't work
with your life. The laws of the universe won't keep the 200 calories from doing it's thing regardless of why you ate it. It's all calories in and calories out. You can find a way to work in things like blood donation crackers, wedding cake, prenatal snacks, etc. and still be successful. It will be part of a lifelong process. So in a way, consider yourself very lucky for not getting freebie points from WW.