Santa's reindeer are like the proverbial postal carriers: neither snow nor rain nor gloom of night can keep them from their appointed rounds. However, just like the rest of us, I'm sure they appreciate a nice sunny day now and then. OhioLINK returns three hits for Raindeer, but one is for a "two-word visual poem for Christmas" by Ronald Johnson called Raindeer Snowbell. It appears to be spelled that way on the original, but it's hard to tell whether it's intentional or not. WorldCat contains 42 records with that spelling. It's likely that errors such as this one, which are more often a matter of not knowing how to spell a word than of simply hitting the wrong key, are committed by the author or publisher, rather than input by the cataloger. You should definitely check the piece to be sure. But don't let rainy deers and Mondays go and get you down.
(Reindeer in the Kebnekaise valley, Lappland, Sweden, from Wikimedia Commons.)