CAPCOM may not of understood your post or may have posted hastily. He does know about processing, just didn't express it fully.
Genetikx, I've not found any change in flavor of sauces made with citrus. However, most citrus juices will change color and darken over time., which can make the sauce look unappealing even though there's nothing unsafe with the sauce.
As CAPCOM was aluding to, if the sauce is to be eaten fresh within a few days of being made, no acidity is needed. If it is to be kept for a while, some form of acidity is needed. Vinegars, citrus juices, powdered ascorbic acid (Vitamin C) something is needed, it's up to you what works.
So back to your original question- yes it is OK to only use lemon juice.