Hmm... if you used all his figures as a guaranty for scale fidelity, I don't think I see a problem with it. But if you're going to mix them in with some resin 1/16 scale kits- are they McFarlane figures 1/16? Best as I can tell, they call them "6 inch scale" and I have no idea what that means, other than they are 6" tall? If they are 6" tall figures, that translates to about an 8 foot tall person if it's 1/16 scale, so I'm thinking 1/12-1/11 scale (5 and half- 6' tall?) ...I think? I'm really bad at scale conversions, I'm not sure on the formula sometimes and I end up winging it.
I can see you being able to work with them if they're 1/16 scale figures as far as switching out resin pieces for... whatever it is their made of? I guess what you really want to know is if they take CA glue or something similar and I'd have no idea. I think if they do and you can get them to match up well, they should take putty fine and if you prime them well, I'd think they'd be able to take paint just as well as a resin figure would.
My brother has a spawn figure or two by McFarlane and as far as I can tell, they are some kind of hard plastic/ruberized vinyl... not really sure, they might label the material on the box, but I know that some of the kits are mixed media depending on what they're trying to represent.
(Also noticed there was one figure with an M14 of course haha that'd helped out with the delima)
Some of these figures look to be between $30-40 a pop though so not sure if you'd be saving money? I don't know what figures you usually get but all of mine are Verlin and they're closer to the $20-$25 range.
I guess it depends on what you're concerned with. If it's saving $ on kits- you might want to try getting some of those old school 1/16 plastic kits from Dragon or Tamiya for under $10 a piece, but if you wanted less time spent over all- it'd make sense to go with the McFarlane's as they come prefinished and most likely look nicer OOB than my finished resin figures ever do and would definitly save you a TON of time.
And hey- just had an idea- if they are a little big for scale- maybe you could throw them in up front and then stick your 1/16 scale guys toward the back (as the scales are close enough I'd think) to where if you played around with the box walls/floors and gave them a little "fun house" kind of treatment- you could probably make it look twice as long, depth wise, as it really is.