Advertise as in buy advertisements for the hubs or advertise as in market them? One could advertise hubs via Google Adwords or other paid options but I don't think you would make money from it.
I choose to advertise my hubs through a variety of free methods like social media, search engine marketing and others.
But I don't do nearly as much as I could, partially because I prefer to use my marketing on more lucrative endeavors, like the blogs I write on.
Certainly, marketing or advertising your hubs is a must if you want to increase your traffic and make more money.