IMO, if you anticipate that your weapon might have to be used under, and hold up to, the worst of conditions, pick one that's designed for and proven in military service.
While the Ruger is a nice little carbine ( I have a stainless Mini-30), and while it borrows heavily from a fine military design, it remains a "sporting" rifle. It never went through the torturous and demanding testing regimen required for an combat issue weapon, nor was it designed with hard use under such extreme conditions in mind.
I like my Mini-30 very much, but if the S were to hit the F, my SKS is the one I'd be taking with me while trying to get away from the spray.
IME, the Ruger is a bit more accurate - for the first three or four rounds. Then POI starts to wander badly and it gets worse the hotter the barrel gets.
The SKS might average larger groups, but I know that I can count on them remaining much more consistant no matter how hot or dirty it gets.
FWIW, if magazine capacity is a factor to you I'd personally rather have 10 rds. virtually certain to function perfectly than any number of "maybes". I've never found any aftermarket high-cap for the Ruger that was completely reliable and only a very few that were even close to 100%.
Ruger refuses to make any mags for the Mini-30 other than the standard 5-rd. model, and the relatively few factory 20 rd. mags for the Mini-14 out there are hard to get and expensive.
For the retail cost of a nice Mini of either flavor your friend could get an excellent condition SKS, accessories such as a sight adjustment tool, chest ammo bandoleers, stripper clips and a reasonable supply of mil-spec ammo, even at today's prices.
If he's looking for the most cost-effective solution, that'd be my recommendation.
