No O/S is needed on any partition/drive...which is not going to be used to run the system. That's why those partitions are called system partitions and only 1 can be active as such at any one time on a PC.
Yes, both O/Ses can see/access any files on that storage drive...after you initialize/format the drive.
Windows (My Computer/Explorer) does not regard a drive as useable...until after it has been formatted.
The Disk Management function will see it even though it's not formatted and you can format it from there.
Formatting Hard Drive - Quietman Guidance - http://www.theeldergeek.com/forum/index.php?showtopic=37155
I suggest that you read all the comments/links supplied by Quietman in the link above, he's a very thorough, knowledgeable person who supplies very complete answers, IMO.