Pea protein is typically used by vegans and also those with lactose sensitivities. There would be no advantage that I can see to mixing the two, unless of course you want to use up the pea protein and can't stomach the taste of it on it's own. The amino acid profile of pea protein isolate compared to whey protein isolate is lacking overall, but by all means if whey is causing a problem pea would be a good substitute. I've used it on and off the last 3 years or so and I am sensitive to whey, even products that are filtered and claim lactose free cause a problem, whereas with pea I get no bloating.