No, Google only allows white hat SEO techniques. I have heard of this grey hat techniques but also heard that Google only allows white hat that is in accordance with its existing guidelines. So, i would like to suggest you that you should have to consider only white hat SEO techniques to get better results from Google search engine.
Gray Hat SEO techniques that can give you a slight advantage, but may not follow Google’s guidelines 100%. This means there could be some risk involved, albeit a low one. These are not to be confused with black hat techniques, which can give you an even greater competitive edge, but carry a very large risk.Gray Hat SEO is about risk versus reward. A large number of SEO solutions are categorized under Gray Hat SEO tools.While some Gray Hat techniques may largely obey search engine rules, others might land you in trouble and need serious consideration and necessary precaution before use.
Gray hat seo techniques, as the name suggests are the mixture of white hat and black seo services. Gray hat rightly said by our respective friend is the risk and reward thing. Black hat seo activities are covered up the by the white hat seo work.