Yes, it indeed is okay to do so. There already is a share button so there is no reason for it to be not okay.
You should also check out the FAQ section about attracting readers: https://hubpages.com/faq/#how-to-attract-readers
-"The main thing to remember when promoting your website is to be a good Net Citizen. Follow the rules and guidelines of the sites to which you post. Promoting Hubs on sites where you are not an active participant can get you in trouble. Also, if you only share your own work, it will raise red flags. Think about how you would like someone to share their work and go by those guidelines."