Running CheckDB on a restored backup is fine. However, monthly is maybe not fine. Do you retain all your backups for a full month? If not, what are you going to do if CheckDB finds severe errors and all your backups contain that corruption?
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