My suggestion is to use the Visibility property of the entire row and hide the row when the corresponding values between the two datasets are identical. I have a sample line of code below, based on the following assumptions (adapt for your actual environment):

a) Dataset 1 is "SQLServerData" and Dataset 2 is "IBMData"

b) The foreign key relationship is a between fields called KeySQLServerColumn and KeyIBMColumn, respectively.

c) The data you want to compare are in columns called TargetSQLServerData and TargetIBMData, respectively.

d) The Tablix in which the data are displayed has SQLServerData as its dataset.

If those were the settings, the following expression could be used in the Visiblity property of the row to hide values when they match:

= Fields!TargetSQLData.Value = Lookup(Fields!KeySQLServerColumn.Value, Fields!KeyIBMColumn.Value, Fields!TargetIBMData.Value, "IBMData")