If a unit has
<IsStartingUnitType>1</IsStartingUnitType>
it must be included in the racetype such as found in CoreRaceTypes.xml
Another solution:
Delete the line <IsStartingUnitType>1</IsStartingUnitType> and it should appear for all races. You can then limit it to particular races using
<Prereq>
<Type>Race</Type>
<Attribute>Race_Type_Altarians</Attribute>
</Prereq>
or whatever is the race for your particular faction
Just a warning, the AI will likely fail to use what you are attempting to do.