It does. It uses the groups defined in entitygroups.xml to pull zombies for the horde.
Example from gamestages.xml.
Code:
<spawner name="BloodMoonHorde">
<gamestage stage="1"><spawn group="feralHordeStageGS1" num="1" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="1" maxAlive="50"/></gamestage>
<gamestage stage="2"><spawn group="feralHordeStageGS2" num="2" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="3" maxAlive="50"/></gamestage>
<gamestage stage="4"><spawn group="feralHordeStageGS4" num="4" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="5" maxAlive="50"/></gamestage>
<gamestage stage="7"><spawn group="feralHordeStageGS7" num="7" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="8" maxAlive="50"/></gamestage>
<gamestage stage="10"><spawn group="feralHordeStageGS7" num="10" maxAlive="50" duration="1" interval="24"/><spawn group="feralHordeStageGS10" num="10" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="11" maxAlive="50"/></gamestage>
<gamestage stage="13"><spawn group="feralHordeStageGS10" num="13" maxAlive="50" duration="1"/><spawn group="feralHordeStageGS13" num="13" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="14" maxAlive="50"/></gamestage>
<gamestage stage="16"><spawn group="feralHordeStageGS13" num="16" maxAlive="50" duration="1"/><spawn group="feralHordeStageGS16" num="16" maxAlive="50" duration="1"/><spawn group="ZombiesNight" num="17" maxAlive="50"/></gamestage>
<gamestage stage="19"><spawn group="feralHordeStageGS16" num="17" maxAlive="4" duration="1"/><spawn group="feralHordeStageGS19" num="17" maxAlive="4" duration="1"/><spawn group="ZombiesNight" num="20" maxAlive="50"/></gamestage>
<gamestage stage="23"><spawn group="feralHordeStageGS16" num="17" maxAlive="4" duration="1" interval="34"/><spawn group="feralHordeStageGS19" num="17" maxAlive="4" duration="1"/><spawn group="feralHordeStageGS23" num="17" maxAlive="4" duration="1"/><spawn group="ZombiesNight" num="24" maxAlive="50"/></gamestage>
<gamestage stage="27"><spawn group="feralHordeStageGS19" num="18" maxAlive="4" duration="1"/><spawn group="feralHordeStageGS23" num="18" maxAlive="4" duration="1"/><spawn group="feralHordeStageGS27" num="18" maxAlive="4" duration="1"/><spawn group="ZombiesNight" num="28" maxAlive="50"/></gamestage>
<gamestage stage="31"><spawn group="feralHordeStageGS23" num="18" maxAlive="5" duration="1"/><spawn group="feralHordeStageGS27" num="18" maxAlive="5" duration="1"/><spawn group="feralHordeStageGS31" num="18" maxAlive="5" duration="1"/><spawn group="ZombiesNight" num="32" maxAlive="50"/></gamestage>
<gamestage stage="35"><spawn group="feralHordeStageGS27" num="18" maxAlive="5" duration="1"/><spawn group="feralHordeStageGS31" num="18" maxAlive="5" duration="1"/><spawn group="feralHordeStageGS35" num="18" maxAlive="5" duration="1"/><spawn group="ZombiesNight" num="36" maxAlive="50"/></gamestage>
<gamestage stage="40"><spawn group="feralHordeStageGS31" num="19" maxAlive="6" duration="1"/><spawn group="feralHordeStageGS35" num="19" maxAlive="6" duration="1"/><spawn group="feralHordeStageGS40" num="19" maxAlive="6" duration="1"/><spawn group="ZombiesNight" num="41" maxAlive="50"/></gamestage>
<gamestage stage="44"><spawn group="feralHordeStageGS35" num="19" maxAlive="6" duration="1"/><spawn group="feralHordeStageGS40" num="19" maxAlive="6" duration="1"/><spawn group="feralHordeStageGS44" num="19" maxAlive="6" duration="1"/><spawn group="ZombiesNight" num="45" maxAlive="50"/></gamestage>
<gamestage stage="49"><spawn group="feralHordeStageGS40" num="20" maxAlive="7" duration="1"/><spawn group="feralHordeStageGS44" num="20" maxAlive="7" duration="1" interval="14"/><spawn group="feralHordeStageGS49" num="20" maxAlive="7" duration="1"/><spawn group="ZombiesNight" num="50" maxAlive="50"/></gamestage>
You'll notice "ZombiesNight" in there towards the end. That'll be why you're getting UMA's.