The original Border Patrol materials included the Gorns as opposed to the Hydrans,
for the obvious reason that the Hydrans, historically, never made it to the
Klingon-Federation border. During the original playtesting, the suggestion was
made that the Hydrans might prove a more interesting variation.
The presence of the Hydrans in Border Patrol is based on an alternative timeline idea
that the Expeditionary Force they sent to Federation Space made it through relatively
unscathed. It also included sufficient cargoes of Hydran technology to enable the
Federation, under Hydran guidance and using the Expeditionary Force's supplies of
Hydran technology, to build additional Hydran units.
Use of the Hydrans is optional for the Alliance. At the very start of the game,
before play has begun, the Alliance Team-Commander may select the Gorns instead of the
Hydrans as the third component race of the Alliance. Once play has begun, this option
is no longer available.