Ugh
No, it's not possible do it in that way [1]. But if you are looking variable number of arguments, that is possible [2].
[1] http://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#user-keyword-arguments
[2] http://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#varargs-with-user-keywords