There's definitely a risk, but I would imagine that in the event of a hostile Egypt that the region would be heavily fortified. In the modern day it would likely be connected by rail links directly to the Roman heartland. And it seems likely that long term Rome would maintain a more powerful navy than the Egyptians allowing them to control traffic through the Red Sea and blockade the Nile delta. A big factor will be what happens with the alliance system in the future. If Ethiopia and Rome stay on good terms a mutual defense pact targeted at a hostile Egypt makes sense. So sure there's a risk that Egypt gets opportunistic while Rome is distracted, but whether fighting the Ottomans or the Latins, it's likely they could sit on the defensive in the Suez, bombard the delta and count on an Ethiopian force working down the Nile.The trouble is the risk of Egypt deciding to block/take the canal for itself. They'd have essentially the same (somewhat fair) arguments for it that the Egyptians had OTL and are perfectly placed to have a go at it. That's a hell of a risk for the Empire to take. Any military force in that region the Empire is going to want control over, and Egypt has very real military potential, particularly if a larger enemy has the Empire's attention.