[bumlebi]

Only if the pressurant gas dissolves into the liquid propellant. Even then, it doesn't even dilute it per se, it just makes something akin to rocket-fuel-soda which causes all sorts of flow problems in your feed lines. Naturally, if your propellant is stored as a gas, adding more gas to pressurize will of course dilute it as you say, but I've never heard of something like this.

So the short answer here is: no, it won't.