Technically if you managed to get to non-hostile relations with remnants they would stop attacking you, just like any other faction. Had this happen in a Nex game, but even there I think it was a bug.
I've heard that NPC patrol captains with high relations ignore contraband or something, but it's so niche a thing that I don't even know how to confirm it.
This is not a bug.
By default, Tri Tachyon is Neutral (0) reputation with all remnant forces. There's even a special dialogue option if you speak to remnants when you have neutral or above reputation with them; you are considered a "Tri Tachyon operator" to them.
You can get this benefit if you commission with Tri Tachyon as you inherit your commissioned factions reputation.
This is the big secret to colonizing in the rim; if you commission with Tri Tachyon, and find a high beacon system, you can colonize there and the remnants will kill all pirates / enemy factions that enter. Double points if you setup your base near the Remnant Nexus, as enemies will gravitate towards it and get owned.