Cats will use the grill cloth as a scratching post. They will not bother the drivers. You can get electrified plastic mats that you can put around the speaker. Any biologic organism that steps on the mats will get an uncomfortable buzz just bad enough to relate to that organism that this is a no go zone. You keep the mats there for 6 months and you can remove them.
If the speakers are cool looking with the grills off then keep them off. Pet hair is heavier than air. As long as the pet is not above the speaker hair is not an issue. Ribbons can be very delicate, you never want to vacuum over them or blow into them. You want to keep a spare ribbon in hand in case something happens. You wipe the speaker gently with a damp cloth.
If the speakers are cool looking with the grills off then keep them off. Pet hair is heavier than air. As long as the pet is not above the speaker hair is not an issue. Ribbons can be very delicate, you never want to vacuum over them or blow into them. You want to keep a spare ribbon in hand in case something happens. You wipe the speaker gently with a damp cloth.