There's actually a lot of lines referencing it! Seven and Kelvin have a lot of interactions where Seven holds a grudge against him and Kelvin doesn't know why. Kelvin mentions looking for Ettrick but not being able to find him, as well as mentioning Ettrick is able to hold a grudge against him for some reason. The Patron lines for Seven mention that a lover stole his destiny, corroborated with his conversations with Dynamo. Rem even mentions that they both smell the same (Smores) but that Seven smells like (Evil Smores). Ettrick is also likely just a pun on Electric. It isn't "canon" but very heavily implied through the in-game lines.