I haven't been participating much here for a while, but I've been a member for a little over 10 years, so I'll declare myself entitled to offer a few comments.

On the basic question, I don't think Elias (or any other member) needs other members' approval to invite newbies.
Yes, the forum will change if new members join.
It will also change if old members leave. It will change if NO members come or go, just because time passes, and we change, and the world changes.
One big problem that ALL online forums are facing: we're running software designed 10-15 years ago for people using desktop computers, but smartphones and small tablets are now the dominant tool for internet access. I don't even own one of the things, but I'm told that forums are not easy to use on the tiny screen. Eventually, forums will have to adapt, or they'll fade away like dialup BBSes.
As for the forum's culture and political philosophy... I appreciate what ML wrote somewhere way above, about how all sorts are welcome here, but... We're a "big tent" that spans the entire range from anarchist libertarian to minarchist libertarian.
Sure, others are technically welcome here, but (as ML also said) they need to have a thick skin.
So, even if we do acquire some Oath Keepers members who are closer to Tea Party Republican, I think there's a good chance that, no matter how thick their skins, they'd find it unpleasant to participate here.
This would also be true if we courted (say) members of the LGBTQ community, or blacks angry about Ferguson-style policing, or progressive Muslims fleeing persecution, or polygamous Mormons, etc. All of the above are primed to hear the message of liberty.
Whether they would actually participate on this forum depends largely on personalities, both ours and theirs.
As it stands now, newbies who choose to stay and participate on this forum must either:
- Already agree with us, or
- Be ready to promptly change their minds and agree with us, or
- Have a giant ego and stick around just to argue with us.
I'm not saying this is a good or bad thing, it's just a fact. Unless the current members agree to welcome dissenters and have a big tent, it'll be a small tent. Small tents are useful things too, but you've got to accept that membership will then be small.