That sounds like prudent advice.
When you're wondering what the seasonal cycle might be for a certain plant (like Stelios was asking, and a question I find kind of fascinating) you have to look first at the climate where the succulent is from. If it is going to have any preference, it will almost certainly grow during the wet season in habitat and be dormant/less active during the dry season. For example, Aeoniums come from a Mediterranean climate with wet winters and dry summers, and they will naturally prefer activity in winter and rest in summer, regardless of how much water they might get in their new homes.
In the case of the Euphorbias, you're looking at a widespread family from all corners of the globe, so there's no way to generalize. A plant from the winter rainfall area of South Africa may rest in the summer, like our native E. misera. But a lot of tropical Euphorbias (from Madagascar or West Africa for example) like it warm and wet, no surprise there, and they often obey a pretty strict dormancy during the off season, regardless of how kind the conditions might be. In almost all other cases, these plants are opportunistic in my experience, meaning they are not strict about the timing of their cycle of activity and rest. Here, where the climate is forgiving... you can't really ask that question in areas with cold.
For what it's worth, Euphorbia resinifera is from a Mediterranean climate area in Morocco (most rain falls in the winter). Here in a climate not too different in that respect, I suspect their behavior matches what you might see in habitat. The main difference is they do actually get a little rain in summer, and we get none.
