The primary reason coconut flour recipes (especially a high hydration recipe like pancakes) end up tasting like eggs is because they are primarily eggs with very little flour.
Coconut flour is extremely absorbent, which means two things:
For the same amount of liquid, you need less coconut flour compared to other flours like flaxseed meal, almond flour, etc. Because you must use less of it, there is less flour "flavor" that comes through to the final product, if that makes sense.
For the same amount of coconut flour compared to other flours, you need more liquid. Because coconut flour has very little protein compared to other flours, that liquid tends to be eggs, which have the necessary protein to provide structure.
Take a muffin recipe for example (I've omitted all other ingredients besides flour and eggs for sake of clarity).
Flaxseed meal version:
- ¼ cup flaxseed meal (28 g)
- 1 jumbo egg (63 g)
Coconut flour version:
- 2 Tbsp coconut flour (14 g)
- 1 ½ jumbo eggs (95 g)
Now let's look at the baker's percentages of eggs to flour in both of these recipes. In the flaxseed meal version, we see that the weight of the egg is 225% compared to the flour (if the flour were considered 100%). In the coconut flour version, the weight of the eggs are 642% compared to the flour.
Something that uses 642% eggs is likely going to taste a lot like eggs. But wait, we're not done yet. Most pancakes recipes are simply flat griddle-cooked muffins, though they tend to have even more liquid than regular muffins. That likely means even more eggs, and egg ratios upwards of 800-900%. At those levels, it's more like an omelette with the coconut flour just going along for the ride.
Whether you can substitute vital wheat gluten (VWG) in place of eggs is really going to depend on the rest of the recipe. Without knowing what the other ingredients are, it's hard to make suggestions. If eggs are the only ingredient providing moisture, then substituting with VWG alone won't work without also adding a source of moisture. My gut feeling is that VWG would tend to exacerbate the requirement for moisture (it's also very thirsty), and tend to make leathery pancakes.