There are two basic techniques for fashioning a 3-Strand Rope to Chain Splice: the nearly-conventional “Chain-Eye Splice”, and the “Plaited” splice. See below for instructions.
WEST Marine performed some interesting tests (See link), which determined that the Anchor-Chain-Eye-Splice maintains about 75 - 85% of the rope’s original strength. This was deemed adequate (with explanation).
What the test did not consider, was the effects of shock over time. These were “new” splices, representing an initial condition. They caution that the splice must be examined often.
I’ve found no tests on the “Plaited” style splice, that your rigger seems to be recommending - although I have often heard it "touted" as a better solution. I suspect it's holding power, and would need further assurances as to it's efficacy.
Don't worry about your rigger's being a "sailor", as they generally have much more "anchor time" than power-boaters. He should have experience with similar sized boats and gear, though.
Rope to Chain Splice Test by Chuck Hawley, West Marine June, 1994
http://www.ussailing.org/safety/Stud...hainsplice.htm
3-Strand Rope to Chain Splice Instructions (New England Ropes)(EYE-SPLICE)
http://www.neropes.com/splice/sp72_3...d_to_chain.htm
How to make a Warp to Chain Splice (PLAITED SPLICE)
http://www.bluemoment.com/warpchainsplice.html
HTH
Gord
To use a thimble ...or not? 
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