The men were conscious when a rescue helicopter arrived but Mr Grayson, believed to be the passenger, died during the flight.
Rally organiser Mark Harris said the rest of the rally participants were told of the tragedy on Saturday morning.
"That was very subdued while they reflected on that," he said.
"They felt that Garry and Michael would have wanted us to continue."
The four-wheel-drive rally, which traverses farm country from Ruakituri to Mahia Peninsula, finished today (Monday).
Now in its sixth year, the fundraiser this year attracted about 200 participants from throughout New Zealand.
Mr Grayson leaves a wife, Gayle, two sons, three daughters, seven grandchildren and a great grandson.
A family notice today said he was a loved husband, dad, grandfather and great-granddad.
The family has asked for donations to the local rescue helicopter trust, rather than flowers.
Last night, rally participants raised about $2800 for the trust.
Mr Harris said he contacted Mr Grayson's wife and brother on Saturday afternoon.
"I still very much struggle with this. I've been at incidents before, I've had to take charge.
"It's heavy when you're busy, but when you come down off that high and your adrenalin comes off, you're not quite sure when you're going to hit the wall.
"When I spoke to the family, I wasn't sure what reaction I'd get, and I've got to say they're just absolutely outstanding."
Mr Harris said he was hoping to visit Mr Finlayson in hospital this afternoon.
He paid tribute to the other safari participants who quickly offered help after the crash, setting off a locator beacon and calling emergency services within 15 minutes.
"We set up a radio chain with clear, good communication to a point where we were able to get contact through the phone system," Mr Harris said.
The injured men were also given first aid while they waited for paramedics.
"People were just absolutely brilliant in that area. We had a nurse and another person there who were recording pulses, and keeping them engaged.
"Unfortunately Garry was our high priority - Michael was a lot more stable."
Mr Grayson's funeral will be held in Hamilton on Friday.
Police and the Department of Labour finished up a scene examination yesterday.
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-APNZ