Daniel is correct. The fields only have to be part of your dataset in order to filter on them using parameters. You do not have to display these fields in your report.
For instance, your dataset query could look like this
SELECT Field1, Field2, Field3, etc.
WHERE CustomerNumber = @CustNum AND CustomerName = @CustName
As for passing the parameter to multiple reports (rdls), each report would have to use a dataset that referenced those parameters. Luckily you don't have to create a separate parameter for each report in your solution. You can re-use the same parameters across multiple reports.
Best of Luck :-)