Unless said person has already prepared for an EVA, it wouldn't matter if they could put on suits unassisted. Because the ISS uses regular sea-level air, astronauts have to go through a tedious procedure in which they breathe pure O
2 and exercise while the pressure is slowly reduced to let the N
2 slowly escape from their tissues. If someone just put on a suit and went out the airlock, there's a good chance they'd get the bends.
One of the big advantages of the pure, low pressure O
2 environment on Apollo was that it made EVAs very simple, at least by comparison. Too bad it's such a fire hazard.
According to
http://spaceflight.nasa.gov/station/eva/outside.html, the protocol is:
1. Breathe pure O
2 at sea level pressure (14.7 psi, 101 kPa).
2. Exercise for 10 minutes.
3. Rest for 40 minutes
4. Drop ambient pressure to 10.2 psi (70 kPa) over 30 minutes
5. Don suit
6. Wait 60 minutes
7. Decompress chamber, presumably while dropping suit pressure to operational level