If the argument against gravel sectors is the likelihood of mechanicals, as Bambi and Trentin are saying, I tend to ignore them. If it's unsafe to ride, there is another thing, but if the problem are punctures, Zwift is now a thing and they can join of the many championships available there, providing they have a decent internet connection.
If the specific section can be crossed by a common car then it's fine for cycling. After all, it's called road cycling and not tarmac cycling, and last time I checked besides tarmac roads we have gravel roads, cobbled roads and so on. Afraid of punctures? Work on your skills, get to know your equipment and gear and have in your mind that a puncture can happen either on a gravel road or going on a flat piece of tarmac riding 60 kph and it's a random part of road cycling as much puncturing on a rock garden is on MTB or puncturing due to bad tire pressures on a muddy course are on a cross race.