Is there a way to view selected images from different contact sheets at the same time?
No, not from separate contact sheets, but you can open multiple folders into the same contact sheet window and then you can view a selection.
Use the Navigator or Favorites to open a folder, then navigate to the next folder and right-click on an additional folder and choose "Open in current contact sheet". You can repeat this as many times as you like.
Now all of the images among several folders will be displayed together in one contact sheet. You can then make any selection you like and preview them.
HTH,
-Kirk