Hi, I don't post much, but just to give my two cents' worth:
I'm pretty certain that there is no default scholarship attached to the Science Scholar Program. Of course, you're eligible for all the usual scholarships (Outstanding Achievement, Exceptional Achievement, Excellence, Excellence and Equity etc.), but so is everyone else with a sufficiently high ATAR / background considerations.
The confusion is probably warranted, however. The official course page, at
http://monash.edu/study/coursefinder/course/1120/ says, "Because this is a competitive program for high achievers, we recommend you apply for a scholarship." From this, I would conclude that there's no scholarship immediately attached to it (though the anecdote at the end does appear to give mixed messages). Also, not all of the Science Scholars in my year have a scholarship, so I assume it's not default.
Regarding the difference between SciSchol and SciAdv, Jinxi makes a good summary. SciAdv is more tailored to those with a research focus (compulsory honours, and a unit about research in 2nd year (SCI2020)). While it is true that one can finish a SciSchol degree in under three years, personally I don't know of anyone who has ever done that (and it personally does not seem like such a big incentive to me anyway).
I think that the only other major difference between SciSchol and SciAdv is a slightly greater degree of freedom of unit selections in SciSchol. Both are still superior to the regular Sci degree in my opinion, because both offer work experience opportunities, a chance to do more advanced units/special research units, and some 'leadership and mentorship' opportunities (and a slight amount of prestige).