If you bought it on PSN then yes.
When you're in the PSN on your Vita, just tap the bubble in the bottom right corner that has the 3 dots. Then tap download history, look for the download and redownload. Just be aware you're only downloading the game and not your saves.
Helpful hint. If Sony does any temporary free downloads for the Vita you can start the download and then quit it and then later when you have room go to download from your history for free.
If you delete anything you downloaded, you can redownload them at any time. This only applies to games though. If you buy a movie, download it and then delete it, you'll have to re-purchase it to download it again.