Can I spell актёр as актор?
I looked for actor in dictionary and found it spelled both ways. Is актор really okay to use?
Well, since you are learning Russian here, use the Russian word, which is актёр.
I guess you could spell it актер since the the two dots over ё is said to be optional unless omitting it would cause confusion (as in все/всё).
Yes, you can spell it "актер" (and actually most of Russian natives do it). But as for "все" and "всё" these are two different words (все - everybody, всё - everything). It is better to write "ё" here to avoid confusion.
It would work if you wanted to say it like you would say it in English, А́ктор. But Актёр is still the right way to say it, if you want to be specific.