Yesterday I received a Hodgdon No. 26 reloading manual that I had found on ebay. I started reading the section about loading for hunting and ran across something I had not thought about and don't know whether it holds water...so I bring it to the vast amount of knowledge on this board.

The person writing the article states several things to do to improve the accuracy of handloaded ammunition to differentiate the end results from plain vanilla reloads.

I do all of those things but what interested me...and could potentially save me alot of time, powder and bullets is that he said (or at least I understood the article to say)once you find the appropriate seating depth for a certain rifle (say .030 off the lands), this will be the optimum seating depth for any bullet you may choose to shoot in that gun.

Is this true?

In my experiance, yes. The best depth "MAY" vary a couple thousanths (+ / - ~.005) but you will be very close.
This is what makes the Stoney Point or other comparator tool so valuable, you can measure any bullet to the optimum depth with no fussing.

In most cases yes, but you throw a VLD competition bullet in there, and it won't. I state this because I have talked to different benchrest shooters, and with their 300 win mags, they seat the SMKs back anywhere from .005" to .01", but when using berger VLDs, they seat them on or in the lands depending on the rifle. Berger even states in their adds to seat their bullets to the lands. So yes, bullets with similar bullet profile, that distance from or in the lands will stay the same, but changing the profile will or can change this slightly.