yeah, in my experience so far, you can buy everything with the in game currency- to clarify, when you're looking in a shop's inventory, for the item's cost it will say something like "$1000 or 25 silver bars", so anything that can be purchased with the silver bars (microtransaction currency) can also be purchased with in-game dollars.
And as people have said here, there are also have plenty of silver bars available to find in the game, so they're not even really a microtransaction only currency, more like an alternative in-game currency that you can purchase more of using real world money. People seem to be reporting that EVERY outpost you liberate has a stash of silver bars hidden somewhere inside- there's a little disagreement over this on reddit, but I have found silver bars in every outpost I've liberated when I actually looked for them.
On top of that, there are ways to make in game dollars super quickly by hunting animals and selling skins (stack up the perk that gives you double animal skins with the backpack perk to let you carry more skins, and use the bow to kill the animals, and you get 4 skins per kill, and can carry something like 10 skins of each animal in your inventory). So even if you don't want to spend time looking through bases for silver bars, you can still make enough money to buy everything if you never find a single silver bar.
But even though it's easy to grind in game money, I actually haven't needed to do it at all yet, I've been able to buy stuff I wanted just from the money I've acquired by playing the game normally. Although to be fair, I haven't bought any vehicles yet, just scopes and suppressors for weapons, so you'll probably need to grind if you want to buy everything.
All in all, a pretty painless and unobtrusive way to include microtransactions.