Is it certain that the receiver of the action is "me" or the one talking?
Also, since the sentence ending is in Casual form, this could be an imperative. What if the speaker is telling/ordering his/her dad to only give a million dollars to another person? So translating this as "Dad! Give only one million dollars!" should be accepted. I'm not sure but please correct me if I'm wrong.
You are quite right. In the absence of an indirect object 줘! can stand for: give to me/to us/to him/to her/to them. With priority set on: "to me".
아빠! 백만 달러만 줘 (= Dad, hand over a million dollars only.) will primarily be interpreted as: Dad, give me a million dollars only.
In speech, to avoid misunderstanding, the indirect object could be placed after the sentence ended. e.g.
아빠! 백만 달러만 줘. 그들(에게)! = Dad! Give a million dollars, to them.
You are not wrong although there is a slight difference in focus between the use of "a" and that of "one". "a" puts the focus on the unit (dollars, in this case) while "one" shifts the focus onto the amount.
It seems however that the purpose of this exercise is to point out that ‘one hundred’ ( & for that matters ‘one thousand’, 'ten thousand' etc. ) is not ‘일백’ ( ‘일천’, '일만 etc. ). The "one" is not translated into Korean.
100, 백 1,000, 천 10,000, 만 100,000, 십만 1 mil., 백만 10 mil., 천만 100 mil., 억