If this actually is your only concern, definitely make the hire. What's great about a concern like this is you can address it in the first 30 days of employment; this is really not a lot of risk for you or your team and finding high-quality people is hard.
There is a lot of risk to the candidate, and you'll sleep better at night if you're up front with the person right before and after you make the offer. People who have never worked at a startup are not going to correctly understand what you possibly mean by "can't make the transition," since parsing sentence in the way you mean it requires experience in both worlds.
So, you have to be willing to be explicit about some of the unwritten rules of a startup (like working until the job is done, never making excuses, being pro-active, getting things done on the cheap etc). This will feel contrary to what you normally do with new employees, as culturally you don't want to be in the habit of telling people "I expect you to work XX hours this week" or "this needs to get done this week by you only and you have 0 budget to do so." During the transition period, however, you do need to be explicit - it will feel weird.
Start by asking them explicitly how they expect a startup to be different than their work experience, then drill down to some hard facts you're guessing they are not going to like. If you do this, they agree to join and they can't comply (or act resentful), you should have a clear conscious when you let them go. Actually, in my experience, if you do this and they can't make the transition, they'll quit on their own in the first 60 days; and (good news) many will actually surprise you with how easily they make the transition - to the point you might be embarrassed in retrospect how much you worried about this.
On the other hand, if this is not actually your only concern, but your way of articulating a vague problem with the candidate you can't quite put your finger on, then slow way down here. You need to do some serious due diligence, and you need to listen to what you are both hearing and not hearing. Do extensive reference checks and pay attention to what they don't say as well as what they do.
If this takes too long to do this and they decide to take another position in the meantime, don't worry about it - you need to trust your instincts when something doesn't feel right but you can't articulate why. Sometimes saying a candidate "doesn't feel startup-y enough" is just a way of saying "even though the resume looks great and I can't articulate what's wrong, I feel something is missing here." Don't talk yourself out of this feeling: instead, research it like a madman. You're allowed to talk to whomever you'd like: get on the phone, now.