Because the other answers feel awfully prescriptivist to me, and I hate prescriptivist cooking, let me give a definitive
You can absolutely substitute a sherry (fortified wine) for red wine in your sauce. The point of adding the red wine into the saucy is not to make it boozy, but to help develop the flavors of ingredients which contain alcohol-soluble flavor compounds, and to add some of the flavors from the wine (though in that recipe, I am going to guess that the wine is pretty much overwhelmed by everything else in the recipe).
Moreover, that recipe isn't particularly traditional (as Tetsujin points out, Worcestershire is really out of place in there; the carrots and celery also feel a bit more French than Italian (to me), and the sugar feels like a kind of weird thing to add). Since you are already making something which isn't super-traditional, I wouldn't worry about crossing some prescriptivist line by further tweaking the recipe.
Experiment, and see what tastes good (and feel free to taste the ragu as you make it).
That being said, it might help to understand a bit what a "fortified wine" (like sherry) is. When a typical red (or white) wine is made, grape juice is fermented over time. In the process of fermentation, yeasts consume the sugar in the grade juice, and... excrete... alcohol, CO2, and other biological waste products. Typically, the process of fermentation stops when either (a) all of the sugars have been consumed, or (b) the alcohol content of the environment becomes inimical to the yeast—this is usually around 15% alcohol by volume (ABV) (or both).
To make a fortified wine, the fermentation process is halted by adding a higher ABV liquor (a distilled liquor, such as brandy) to the wine. Adding the extra alcohol makes the environment hostile to the yeast, and prevents them from further fermenting the beverage. The result is that not all of the sugars are consumed by the yeasts, so the end result is boozier (higher ABV) and sweeter.
In this ragu recipe, the booziness is not really an issue (the red wine is probably around 12-15% ABV, the sherry is maybe 18-22%—a noticeable difference if you are drinking it, but likely a small difference in this recipe), but the sweetness could be. My recommendation would be to remove the sugar from the recipe and substitute the fortified wine for the red wine, one-to-one.
Alternatively, you could just leave the wine out entirely. After a long, covered simmer, the recipe calls for reducing the ragu until it thickens—if you start with less liquid in the recipe, this will go faster. You will almost certainly lose some of the complexity of the flavors—you could rejigger this by, for example, adding some beef stock or vinegar (like, just a little vinegar), but you might not find that necessary.
And, again, taste often. As you are making the sauce, taste it. See if you like it. Adjust as you go.
P.S. Ignore Tetsujin vis-à-vis the Worcestershire. My Jewish mother insists that it is part of a traditional recipe, and it's delicious. :P