Sure it's necessary. CheckDB checks to see if there's any corruption of any form in the database. Invalid checksums, bad page linkage, out of range column values, etc
I would suggest you run it before the backup, and maybe not backup the DB is there's corruption. A backup of a corrupt database is not very useful
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability