I believe that as long as the pranks are appropriate for the workplace then they are fine. April Fools' pranks are a harmless tradition, and it's always nice to be able to let your inner child and mischievous side out for one day of the year. As long as nothing harmful is done, it should be fine.
As long as the prank that they choose aims to not offend anyone and is not dangerous in any way, there is nothing unethical about it. In fact, pulling a great April Fools Day prank can be a great way for a company to get people to notice their company and get potential customers talking about their product.
As long as the prank is nothing harmful financially or physically towards their customers then I think it's fine for a business to pull an April Fool's Day prank, I believe most people enjoy the little jokes and events that happen from businesses on this day and can understand it's a joke.
Personally I am against April Fool's Day pranks as well as I am against the whole April Fool's day concept because I think that all these pranks are just a way of encouraging disrispect among the members of our society. We just should not play pranks agains each other because this only generates violence