Were xenos a part of the Galactic Empire

[Ekaton]

As in the title, I’m about to start my first campaign on a planet with sentient aliens and I thought, were any sentient aliens considered a part of the pre-collapse republic?

[BlueTemplar]

From the manual :

[...]
The Galactic Republic was a predominantly human empire. Any alien
space-faring empires where either bypassed or destroyed (if they were proven
violent). These alien empires encountered were initially relatively small until
the contacts made during 7th to 8th millennium.
Some of the lesser developed alien races developed culturally during their
“occupation”, some of these species acquired full citizenship of the Galactic
Republic, some tried to fight guerrilla wars, some gained independence and
their own system(s).
The empire [Not Republic ??] resembled a shape not unlike that of a wheel of Swiss cheese.
The holes in this cheese are representing the alien cultures.
[...]
It was in the 8th millennium that the Galactic Republic’s continued
expansion outwards started to slow down. The first cause for this slowdown
was the encounter with several strong alien dominions that blocked obvious
routes to further human expansion.
[...]

[laagamer]

I prefer the Xcom method of xeno-negotiations.