Kerri,
The simple answer would be to say "No. The WBS is not listed as an input to all risk processes". But...
Please check your PMBOK Guide on page 274. You'll see that it is not listed in any as an "official" input. When you read through the inputs of the processes you will, however, read that it is sometimes still mentione. (i.e. the Scope Baseline which contains the WBS is an input to Identify Risks.). So the WBS is definitely used in some of the processes.
So it's used in some, but not officially listed for any.