You're going to have to rephrase the question.
I'm not really sure what you're getting at.
If you are referring to the schematic above, then the emitters of Q1 and Q2 are tied to signal common, which is the negative side of the power source.
I'm not sure what you are getting at?
My initial reply was to a post by ElectEnthusiast, where he said:
The signal is applied to the base. The Collector changes its current response directly in correlation with the received signal. Therefore, the signal does not see ground in this scenario.
I really shouldn't be calling Q1 and Q2 a differential pair, you can argue that the Emitters should be tied together AND loaded by some variety of Current Source to be properly called a Differential Pair.
Again, I say "Groan".