Early in Union History the only non human member were the Ult, but they could easily adapt to human environments and requirements. There were even voices within the young Union to prohibit non humanoid species membership.
These voices never gained more than 2 % approval at the Assembly, and the book "Armed Forces and society: problems of non human alien integration" written by Army Colonel Aaron Wetherby drifted into obscurity almost as soon as it was written. But the book actually did rise many valid points and Ult Admiral Wapp Smokes who is considered by many the father of the Union Fleet used the book to define the basic physical requirements for a being to be able to serve in the Navy. The Marine BaPhy regulations are a direct result of this book. It also details the problems and challenges of a commanding officer to find fair and balanced tasks and assignments to both human and non human beings.
The book is now required reading material for all Union Command Officers and command candidates. Because the issues also work vice versa: for a Non Human Command Officer with human crew members.
The book is part of the so called Captain's Treasure and every Union Captain must know it by heart.
 Admiral McElligott was and is the Administrator, Stahl the warrior but Admiral Wapp Smokes organized the details. How a Union Fleet is organized, basic and general orders and a million other details needed to form a successful Navy came from his mind.