It seems the default live raid window is already using this, so I would assume it is showing the correct name for the correct location.
Code:
<Icon DynamicData="/GameData.Raid.Member_0.Speaking" IconRect="124,204,135,215" IconResource="/images/widgets01.dds" Location="3,3" Name="Speaking" onpress="vivox_adjust_volume Parent.Name.FullName" ScrollExtent="10,10" Size="10,10" TreatAsButton="true" />
<Text AbsorbsInput="false" DropToParent="true" Font="/Fonts.FontArial13" Location="15,1" Name="Name" PackLocation="top,left" ScrollExtent="75,16" ShadowStyle="/ShadowStylesNew.Drop.style" Size="75,16">:5fd3b538acb4e75c:Longestnameposs</Text>
Or else the Vivox engine is smart enough to strip the prefix when needed as well. Guess I'll try it tonight and see what happens.
EDIT: Seems to work fine on a normal server and doesn't require the previous hack I made up.