I think the problem with that keybinding is that it isn't actually part of the terminator part of the code, it's part of the terminal (which is vte, or something underneath). Any keybindings that are for the underlying single terminal are not configurable in terminator (which just does the multi-terminal parts, and adds slick plugin features, etc).
I did find that if you use the default setup, the single line scroll only works for the numpad up/down. The reason is that Up is tied to resize_up (similarly for down). If you remap those keys, then you can use the regular arrows to scroll by one line.
It would be nice to find a solution for changing the keybinding in the underlying terminal, but in the meantime, if you want the regular arrows to work, just remap the resize_up and resize_down keybindings.
tested in 0.97 ubuntu 14.04.
2If you want to be able to scroll line by line as I did, you can use CTRL + SHIFT + Up/Down keys. – Haggra – 2016-11-05T17:12:59.373