I think for the USA you have

I think for the USA you have answered your question. In Canada the situation seems a bit different. I haven't found the exemption1) and 2) in Canadian rules instead yard engines are exempted: https://www.tc.gc.ca/eng/railsafety/rules-tco76-338.htm

Scroll down to 16. Illuminating Devices.

And here is proof for the saying there is a prototype for everything, a Port Stanley Terminal Rail GE 44t with ditch lights: http://trainiax.net/photos/2007/2007-07-05-pstr/photo-pstrl3-1-2007-07-05-pstr.JPGand another one with its train: https://www.railpictures.net/showimage.php?id=495311&key=7283864

That is the only one I found so it is not the rule.
Regards, Volker

Investigation

Dear Kirk,

Intriguing question, lets go for a walk and see what we can find...

A quick Google search concurs that there are few contemporary 44-tonners running around with ditch lights,
(although that could well be just a factor of what pics have been uploaded online and crawled by G),

It would appear that Museums and Tourist Railways are the ones "most likely" to retrofit ditchlights on a 44-tonner.

Examples

Southern Prarie Railway

Newport Narragasset

Port Stanley Terminal RR

What we can take away from this is:
- mechanically/electrically, it's entirely possible to equip a 44 with ditch lights
- above or below-deck/frame level lights are both possible

If we limit ourselves to contemporary industrial and in-plant 44-ton switchers, then yes, ditchlights seem more "optional" than "mandatory"...

Nucor Steel, Seattle

Southwest Metal

Modoc RR Academy

AgriCo Florida

ADMX

Upshot, it's your choice, you could justify either ditch-lights or no,
but the key factor may well be whether you want-to/can-wire and decoder-config with a spare 2 or 4 outputs to make them work?
(Discretion is a modeller's friend in many cases...)

Further reading/investigation

http://www.rrpicturearchives.net/locoList.aspx?mid=214

https://www.railpictures.net/

https://www.locophotos.com/Search.php

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Thank you professor !!!

I looked for shots like that and simply could not find them. 

I'm not sure I like the way they look. Maybe, I will leave them off?  Then again, it would be truly unique. 

The Narragassett unit looks unique with the horns and the RV air conditioner

I too must have looked in the

I too must have looked in the wrong places finding just one.
Regards, Volker

Green 44 tonner

The green 44 tonner (Nucor Steel, Seattle) really gets the modeling juices flowing.  A green diesel in a grey world!  Is that photo contemporary or historical?

I'd vote for no ditch lights!

Robert

Nucor 44 tonner

That is a nice looking little critter.  That photo above appears to be a screen grab from this youtube video, which was filmed 1/16/2010.  Wether that’s contemporary or historical depends on your viewpoint I guess.

If you search around youtube there are other videos of the same critter.

Nucor has excellent examples

I don't really model the steel industry, but if you have a model that you "just have to have" but can not find a prototype, travel to your closest Nucor Steel facility and you are likely to find something interesting. Old flatcars, ancient switchers, unique signals... on and on...

By GCOR

By the GCOR rules as of a couple years ago (when I retired) the absence of ditch lights restricted the move to no more than 20 MPH over a public crossing. Other than that, you could run like the blazes.

I do recall early on my company I worked for had a couple or so engines not equipped with rear ditch lights. Sucked to use one a 20+ MPH main line when running long hood forward.

Andre

Since I model the 1990s into the early 2000s,

The first engines I recall seeing locally with ditch lights were the new SP GP60's ,so around 1990 ditch lights were a pretty new thing. You'd have to look up the implementation date of the rule that required ditch lights to know if they'd be required on all engines by early 2000's. I doubt an owner would add them to a 44 tonner if it wasn't required at that time. Tourist line  engines are not a good guide for engines of the past era, as they are modified to suit the present use and rules.....DaveB