1. The chain on one of these bikes is not going to last as long as a bike with less severe duty.
2. The chain on any bike with a single cog drivetrain can stretch significantly farther than the chain on a derailleur bike.
So: if it's not skipping under load and you can't pull it off the chainring, it's probably fine even at more than 1%... however you want to measure that.
I've seen quite a few of those wheelchair transports on charity rides for MS and Ataxia.