It's a overlay blended over; And yes, you can apply it to other LH, there are however a few limitations - i.e. You can't apply it to
some LH - it's applied globally, so it's either all or nothing, as far as i can tell. (Edit: Maybe it's possible to merge the effect on a single nif using NifScope, but i expect the anim (noise) to get lost )
Also some Backgrounds will look odd.
Look into Civ4ArtDefine_Misc.xml...
Code:
<MiscArtInfo>
<Type>REPLACE_LEADER_BACKGROUND</Type>
<Path/>
<fScale>1</fScale>
<NIF></NIF>
<KFM></KFM>
</MiscArtInfo>
<MiscArtInfo>
<Type>REPLACE_LEADER_FORGROUND</Type>
<Path/>
<fScale>1</fScale>
<NIF></NIF>
<KFM></KFM>
</MiscArtInfo>
These are from unmodded game, if you look into FF you will see a SpaceLeader.nif (or similar, not remember exactly) assigned here.
This nif is partially transparent and has animated noise, so blending it over will cause that holo effect.