May I ask for clarification? Am I correct in thinking that if I enable iCloud Photo Library that I will no longer have the option of deleting photos from the SD card after an import?
My answer does not apply for importing from a card or a camera.
You can use iCloud Photo Library on your Mac or mobile device, and still delete from a card directly after importing, if you want.
However, it is not recommended to do that. We have seen many reports here in these forums, where photos have been imported to iPhoto or Aperture, and have been deleted directly in the Import panel, that went dreadfully wrong. In rare cases it can happen, the system crashes at that critical moment and the photos will have been deleted from the card, but do not yet appear in the photo library. Or some photos may not have been transferred correctly from the card, because of some I/O error. It is risky to delete the photos from the card, before you have checked all imported photos individually and then made the first backup of the imported photos or your photo library.
When you are sure, your photos have been imported correctly, delete the photos from the card by deleting all photos in the camera at once, or by reformatting the card. I simply keep the photos on the card as second backup, until all cards are full, then I reformat the card.