We need to be careful with the phrasing here.
If the PC can see the phone by Wifi or USB cable, the phone will let the PC see most of the SD card, just like the phone's file browser can see most of the SD card, subject to the android file system security.
If you want to see the SD card contents without the android security, you need to use a card reader.
Glossing over the details, yes, you can use your PC to copy to and from the SD card for the most part.