Yes, several members of the delegation were there only for the political implications of their inclusion. This included a soldier named Nicholas Bieliakov, a sailor named Fedor Olich, and a worker named Pavel Obukhov. None of these men were really intended to do anything beyond being a statement. As you note though, a peasant was lacking, this key demographic being overlooked.

An old man named Roman Stashkov, described exactly the way you probably picture an old Russian peasant, was found walking in Petrograd while the delegation was driving to their train, and quite literally picked up off the streets. He identified himself as a Left Social Revolutionary, so was politically agreeable enough to be included, and they took him into their car. He was somewhat cajoled into going at first, being told they would 'give him a lift' to the train station, as he was intending to go to Moscow, but was convinced by payment.

At the negotiations, he of course did nothing productive, and had little idea what was going on anyways. He reportedly would sometimes slip up from using 'Comrade' and instead call the other members 'barin', the old honorific for 'Master'. He was quite the hit socially though, guzzling down the food and drink, and even amusing the Germans somewhat with his earnest simplicity. Reportedly, seated next to Prince Ernst von Hohenlohe, he asked his neighbor for advice on which wine to drink - red or white - as he wanted the one that would get him drunk faster.

Brest-Litovsk: The Forgotten Treaty - John W. Wheeler-Bennett

A People's Tragedy by Orlando Figes