Can I configure DR with single new node?

Here is a link to the the Best Practices for Disaster Recovery doc page for Vertica 9.0.x:
https://www.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/AdministratorsGuide/Recovery/BestPracticesForDisasterRecovery.htm

If you stand up a single node for DR you'll have to mamually copy/load data onto it as replication and back up /restore won't work because you have to have the same number of nodes.

Replicating Tables and Schemas to an Alternate Database
https://www.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/AdministratorsGuide/BackupRestore/ReplicatingtoanAlternateCluster.htm

Creating Full Backups
https://www.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/AdministratorsGuide/BackupRestore/CreatingFullAndIncrementalBackups.htm

Restoring Full Database Backups
https://www.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/AdministratorsGuide/BackupRestore/RestoringFullDatabaseBackups.htm

You can use Vertica's IMPORT/EXPORT functionality to copy the data from the 3 node DB to the 1 node DB:

Importing and Exporting Data Across Databases
https://www.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/AdministratorsGuide/CopyExportData/CopyingAndExportingData.htm

P.S. You might want to plan to upgrade Vertica in the near future

Newer features you are missing out on:
https://www.vertica.com/docs/9.1.x/HTML/Content/Authoring/NewFeatures/_VersionIndependent/NewFeatures.htm
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/NewFeatures/_VersionIndependent/NewFeatures.htm
https://www.vertica.com/docs/9.3.x/HTML/Content/Authoring/NewFeatures/_VersionIndependent/NewFeatures.htm
https://www.vertica.com/docs/10.0.x/HTML/Content/Authoring/NewFeatures/_VersionIndependent/NewFeatures.htm