Gord has no idea how dangerous the Black Riders might be. It sounds like they could have killed this party and didn't, several times; they might be herding it somewhere with their fear spells; but if a fight develops and they see a real combatant on the halflings' side, he doesn't know what they're capable of. And there are five of them; even if all they have is longbows (magic longbows?) they'd have the advantage.
He doesn't know why they're after this party. Not wanting to fight a losing battle does not necessarily make the halflings good or righteous. Perhaps they did something to the riders that they seek to avenge; perhaps they are planning something that the riders seek to avert; perhaps they are only waiting to link up with their stronger allies (the wizard Gandalf?) before turning the tables on the riders.
Frodo has a magic ring of great power, but the Riders don't seem to be after it or they'd have taken it already. Hiding only goes so far, and a wizard who can cast fear spells ought to be able to cast Detect Magic and Locate Object too.
If Gord was infinitely powerful, he'd protect them until morning, with no casualties on either side, and then talk to the Riders (after they'd seen him help their enemies) and decide which side to help, if any. But he's alone in a strange world and up against unknown enemies who outnumber him five to one - he's not really thinking of this party as combatants anymore - and this plan is insane and frankly suicidal. He can make a very good showing for himself if pressed, but that means less than nothing when the enemy is unknown.
He doesn't have a spell prepared that would let them all hide for the night, like a wizard's rope trick; he'd have to actually fortify and defend a position, and these people aren't even competent to tell him what their enemies are really capable of when pushed to it. He has his daily nondetection, and other tricks to help him sneak away, but they're only enough for one person; he was traveling alone and didn't prepare any party buffs, and the only thing he has that would affect them all is that useless mass disguise other that only works for a few rounds. He has his bag but only one air bubble and even that only lasts for a few minutes.
Even if he led them away from here, he has no idea how the Riders have been tracking this party and the middle of nowhere, in the dark, would be worse to fight in than a prepared position.
He really, really ought to sneak away now and return tomorrow morning.