I am replacing my rotor for my charging system and the new/OEM replacement rotor is thicker than the original in that when I put them on a table face down side by side the new one stands taller than the old one. Do I need to use the alternator spacer with it?

 

How much taller is it? ten or even fifteen thou probably not an issue, quarter inch probably is a big issue.You can measure them with calipers, or a micrometer, if you are familiar with these tools Otherwise, there is insufficient information to really have an idea.