I am using EWS Java API ver 2.0 jar and does not have the Enum value Exchange 2016. Would it be still fine to connect Exchange Server 2016?
You can connect with any earlier ServerRequest value, as long as you don't need new version 2016 features.
Should you need explicit 2016 features, than you have to use the values in my self-answer to the question Name of Version property in ServerVersionInfo element for Exchange Server 2016?.
(And note the reference to answers under the related question Exchange server version “V2_22” returned for Office 365 breaks pattern - consequences?)