There are numerous places and reasons where sparks are towed by DEL's, Mel takes sparks to Ballart all the time. Cityrail has been known to have its failed trains hauled by DELs and I believe during Syd 2000 Olypmics they had DEL's stored around the network to get in and move a failed unit ASAP if required and I have known it to happen in Qld, including the RTT which at times has to get towed through a failed section of the O/H. I'm not sure on the mechanics but 1-2 locos hooked to the front, probably two if older models and make reverse operation safer, adaptor on the coupler and what ever for the brakes and away you go.
Day or night, who gives are rats, most of the public certainly will not. Is it a bad look? Why would it be, especially if it was to the maintainence sheds where they are often towed anyway to avoid the need to have O/H in some buildings.
A dead EMU is about 120-130t, or a bit more than a NR class, I would not have thought is a heavy load without brakes for even a pair of older DEL's, especially if driven under caution and limited speed.
If the braking system is not capatilble I'm sure there are more ways to skin a cat, however if the said locos would be used routinely, which by the sound of it they would be as there is a very limited size BG fleet of locos available, permanent mods can be done to enable this. I've seen the Qld RTT towed by a single 4000 class they dragged off a coal train. the auto coupler adaptor is on the RTT as I believe its also on the XPT, so I highly doubt there needs to be extensive mods to a DEL to haul a dead EMU. Certainly in rescue mode there is limited scope to top and tail a dead EMU, esepcially on a single track line or a double track a long way between cross overs and even more so if there are other trains trapped behind.
End of the day, its not a big deal or a bad look!