There are definitely more than five nominees in Doctor Who history.
Sophie Okonedo, Carey Mulligan, Pauline Collins and Imelda Staunton were nominated for acting Oscars. Sir Ian McKellan was nominated twice. John Cleese was nominated for a best original screenplay Oscar for A Fish Called Wanda. Peter Capaldi actually won, albeit not for acting. He won for his live action short film, Franz Kafka's It's a Wonderful Life. And, depending on one's view of who counts as a "Doctor Who actor", Jim Broadbent, who played the Doctor in The Curse of Fatal Death, won a best supporting actor Oscar for Iris.
So that's at least eight. But if you really dug around, and were inclusive of the Big Finish audios, you could probably shake a few more from the trees. For instance, Oscar nominee Frank Finlay has appeared in Doctor Who, but only in the Big Finish play Bedtime Story.