Hi Craig
I believe it is possible, but one thing you have to watch out for is that a pivot table allows a maximum of 32,500 unique items per field, so if your 4 sets of 25,000 records exceed this (eg because each record has a unique ID) you won't be able to create a PT using this field.
Otherwise, I would recommend using the External Data Source option for the source data and using MSQuery to consolidate the records. Post back if you need help on this.
Richard