Is it safe to break open my vistaril (hydroxyzine) capsule before swallowing?

Yes, if you like: Medications are encapsulated primarily to make them easier to take, although sometimes the capsule serves to deliver the drug to the intestines, not the stomach. Vistaril (hydroxyzine) is also available as a liquid (web search on "vistaril package insert"), so the capsule doesn't serve any purpose other than to prevent you from tasting it. If you can tolerate the taste, you can open the capsule.

Yes: Not sure why you want to, but this should work fine if you don't spill any.