Sure, making a sugar syrup is fine, too. It's accomplishing the same thing (dissolving the sugar completely) just in a different way.
Personally I'm not up for the hassle of making a separate syrup, storing it somewhere, etc., since it saves me no time over dissolving the amount I need, right when I need it.
But there is no rule about making it ahead, nor any rule about whether to combine with the lye solution or the oils, or to add before trace, or add after trace. Everyone is free to do what works best for their soaping style. That being said, generally, the fewer things you must remember to add after trace, the better. Plus, once your CP soap reaches trace, if you are hoping to make designs, you are now working against the clock and against chemistry when you start stirring in more stuff. Now, if you are making HP and not CP, then adding hot sugar water at trace is wonderful for making the batter more fluid. Thus, it's important to know the context of the recommendation because what helps in one situation can hurt in another.
For all of the above reasons, it's best for me to make my dissolved sugar (sorbitol) solution when I'm making my soap, and to combine it with my lye solution, or with my oils, before making the batter. That way, I don't forget it, and I don't affect my level of trace by adding something in later. But you can and absolutely should do it differently if that works better for what you are making, for how your brain thinks, etc.