I've been in two startups with international teams - technical ones in different countries.

I agree with the other answers here that technology now is superb at helping people keep in touch - e.g www.slack.com - so collaboration is much easier. You need to make sure they're always part of the team and feel involved. I know one company who puts a tv screen in their office and has a live Skype video feed playing at all times so everyone can see each other.

Just be careful about giving them the VP or CTO role though as ultimately that person will be building the tech team and they'll only be able to do that back in the US... so if you're happy with all team being there then that's fine.. else Senior Developer is flexible enough.

What ever you decide - get them either on a contract basis or bring them into the team with equity - but make sure it has a good vesting clause (i.e. they earn shares every 3 months until the agreement is terminated).