Death Eaters have no need of Patronus charms.
From this interview with JK Rowling:
Samantha: Was snape the only death eater who could produce a full patronus
J.K. Rowling: Yes, because a Patronus is used against things that the Death Eaters generally generate, or fight alongside. They would not need Patronuses.
Quote to support the above assertion, from Lord V talking to his recently recalled Death Eaters in Goblet of Fire:
Voldemort moved on, and stopped, staring at the space - large enough for two people - that separated Malfoy and the next man.
'The Lestranges should stand here,' said Voldemort quietly. 'But they are entombed in Azkaban. They were faithful. They went to Azkaban rather than renounce me…When Azkaban is broken open, the Lestranges will be honored beyond their dreams. The dementors will join us…they are our natural allies… we will recall the banished giants…I shall have all my devoted servants returned to me, and an army of creatures whom all fear…'