Firstly let me tell you one thing, Java is the base language for Native Android Application Development but that doesn’t mean you have to be proficient in Java to start working or learning Android Developer.
If we talk about Android Application Development then all the Code is written in Java (Core Java) and OOPs concepts. To start learning Android Application you must know basics of OOPs, basic concepts of Core Java just like inheritance , overriding, creating classes, creating methods, method overloading , interfaces etc. And you should have basic understanding of XML (how XML looks like and you can understand that).
So if we go back to your Question. Yes we do need to know basic of Java and No we don’t need to be proficient or very good in Java.