No, they would for certain see the Infernus. Model/texture replacers are purely clientside - they have absolutely no effect on the game outside of what the player with the mod installed sees. Other players would see every Infernus as an Infernus, and the player with the mod would see every Infernus as a Murcielago.
I'm not entirely sure of how a purely clientside model replacement would work in terms of vehicle damage, since the model would have to retain the same 'hitbox' as the Infernus, and I'm fairly certain that the car models ARE the hitboxes in GTA.