As the PP said, you may or may not be accommodated if you show up with an extra person. If it was an unpopular restaurant, I would say the chances are pretty good, but 'Ohana is very popular and tends to run behind schedule anyway.
I would keep looking for an ADR for with 5 or 6 people. It's a well known glitch (at least here on the Disboard), that the Disney ADR system doesn't always see an odd numbered party as the same as the even numbered party (i.e., it doesn't know that 5 people can sit at a table for 6). So you might find more availability if you bump up to the next even number. I've had to do this before when hunting for a table for 3 (no availability for 3, but there was availability for 4).