Sure, you can put anything you like in the header.
So all you need to do is;
a) create a small procedure or routine to loop through the view, counting the number of records that are in the result set. This may be a tad expensive from a time point of view, especially for TPS. For SQL you might rather construct a Prop:Sql statement to count the items in a result set.
b) use this procedure to prime a variable, or use it directly in the header.
Of course if you change the browse filter then you will need to re-calculate this number and refresh the header.
Personally I think the "cost" of calculating this number is too high.
cheers
Bruce