Yes, it is allowed to do it this way in order to achieve backward compatibility with previous Java versions.
And no, you don't want to code like this.
Consider the following:
The compiler would be happy to compile this, but guess what you get in List<String>? An object!
By declaring a Collection<String>, you want to be sure that you get only Strings in there, while a raw type collections allow you to add anything. One day after refactoring your new ArrayList() will be returned from a separate method. Maybe the next day someone will add something to it and who knows, maybe this something won't be a String...
Honestly, there is no real difference, but the only reason the second version is allowed is to make it easier to compile code that uses generics with old code that does not. It's just better style to include the <String> in both places.