depending on what you use on the teak to clean and restore...and how careful you are about the product application.. SOme will stain badly any fiberglass...others not so much. I always start at the top and work down, masking, shrouding and taping off any finish I don't want this stuff on. Clean up any spills or drips sooner than later....once that is done then go with glass polish or compound. Unless you are a pro, stay away from electric/air buffers as they will eat/burn through finish very quickly.
All the best. Enjoy your Sabre, my 38 was one of the best boats I ever owned.