Lucid...
I see where you are coming from, but respectfully, i dont see the problem being worse with red use.
Guild ganking in fel is the problem, regardless of it being reds doing it or blues.
Instead of a check for criminal, what about something like a time limiter... you can only goto or bring a guildmate if you havent already done so in the last x minutes?
If the DateTime is a single value for both then only one person could come in aid. One person incoming for each person already there every x minutes.
If the DateTimes were stored separately <goto> <bring> you could allow a faster, but still controlled influx of aid. Two players incoming for each person already there every x minutes.
#Edit:
I saw Supernova's suggestion as a good limiting factor.
If blues are in fel... they already chose to be there and accepted the possible outcome of dying.
Also, this suggestion moves the guild wars battlefields to fel if the guilds want quick travel, thus adding in the possibliity of reds getting in on the action
#end edit
Guildmate travel does create a change in the fundimentals of guild wars, but that was part of the intention...
Guildmates having the ability to quickly aid guildmates.
Also:
One thing that has probably been overlooked that i saw in scripting this is the possibility of going to a recently dead player to avenge them.
Will the permission gump open for the dead player? I don't know, havent checked.