Once the correct portal is opened, travel is bidirectional and you can totally send someone in to help your away team.

yeah, i've been doing this for awhile. If someone starts cursing or screaming "i need cleansed," i run through the gate.

Last week, we played with a raid virgin, and someone with bad internet, so there was a lot of times where we'd run through the portal if the "wrong" people got teleported.

Especially useful if things start getting hairy, cleanse isn't working due to lag, or your Aegis-holder bites the dust and is replaced by an Oracle slayer (costing you a pair of hands).

I assume this is a known technique, but Ive never seen it mentioned, so thought I'd share just in case.

EDIT: They also seem to stay open during Time's Vengeance. An opportunity to run to the other portal and revive anyone who's been screwed by those dodgy portals sending them to the wrong place. An awkward but functional solution until its fixed (please, Bungie).