Go ahead and register, and ask the hostess if she can let folks know you registered -- but that you're fine with guests not using the registry either. If you and the hostess are good friends and you express to her exactly what you wrote here -- that you're concerned folks will see this as begging -- I bet she'll say, don't worry about that!
Sure, you have three other kids, but I don't know their ages, and you may need things that you had with them but have gotten rid of already -- stroller, diaper bag, "diaper genie," feeding necessities, etc., and of course there are always diapers and more diapers you can put on registry. I don't see registries as begging or asking for frills. I would rather know what the parents really do need so I can be sure my gift will be used. And anyone who wants to go "off registry" can do so, and you'll smile and love those gifts too. Enjoy your shower!