He had two-hundred dollars.
He lived for one-hundred years.
I have never put a hyphen before hundred in situations like those, but according to this (unsure of its reliability, however), it says:
. . . one-hundred dollars is hyphenated because one-hundred is a compound adjective standing before dollars . . .
From the example since “xxx-hundred” is modifying something (dollars/years), making it an adjective, should I therefore put a hyphen in between?
It is not an adjective in those expressions, and is not normally hyphenated. Your source is wrong in describing it as an adjective.
It is a quantifier, which is grammatically quite different from an adjective.
On the other hand, suppose a casino has chips of different denominations, one of which is 100. Then one might speak about “a one-hundred chip”: in this phrase, it would be adjectival, and so hyphenated. This is quite different from “one hundred chips”.