Hi Ferris Ferret,
Protein during exercise is a relatively new area of scientific interest. Some research suggests that muscle damage is reduced after exercise when protein is included in the fuelling regime, however, no performance advantage has been shown in studies in a temperate climate. Some studies looking at protein added to carbs when exercising in a hot environment however have found a performance benefit which they believe is due to an improved thermoregulation. There has also been a suggestion that digestion is less impaired over a long event due to a possible protective effect on the gut (this has been suggested for collostrum too).
My take out from this is that as the response to fuelling is very individual, it is worth considering taking on protein in your carbohydrate drink if you digest it well and have tried and tested it in training. If you're in a hard training block then potentially the protective effect on the muscle could support recovery from workout to workout and if you're racing in the heat you could potentially reap the most benefit.
Hope this answers your question. Lynn.