In testing, my trading partner told me they were expecting 20150818 (date with century) in the following bold field.

GS^SH^BTS-SENDER^RECEIVE-APP^150818^1212^2^T^00401~

The GS indicates this is the “GS Segment”, the fields are numbered GS01, GS02, GS03, GS04 etc… based on the separator character, which in this case is the Shift-6 carrot symbol.

In BizTalk, this field is NOT mapped by the developer.  Instead, the EDI functions of BizTalk creates the line and formats the data on it.

You have to set up Parties in the BizTalk Admin console to use EDI in BT2010. Then you create an “agreement” between those two parties.
Select the agreement, click the proper tab on the top (I had to blur out the company names), then click on the “Envelopes” option on the very lower left.
Scroll right until you find the GS4 segment, then select the desired date format.

You can also type in the desired GS02 and GS03 values above.