National police spokesperson Vishnu Naidoo said the suspects are "the masterminds" of a syndicate believed to be involved in rhino poaching across the country.
"The arrests were a great breakthrough for us. More arrests may follow," Naidoo said.
Dr Karel Toet and his wife, Marisa, were arrested early on Monday morning. Dr Manie du Plessis, one of Toet's partners, was also arrested.
They own the Nylstroom animal clinic, as well as Limpopo Wildlife, which is involved with catching and transporting game on farms.
Naidoo said two businessmen - as well as the one businessman's wife - were also behind bars. The other suspects' occupations are unknown. They were arrested in Polokwane, Musina and Modimolle respectively.
"These people were supposedly involved with killing rhinos, selling the horns and disposing of the carcasses," said Naidoo.
This breakthrough comes after five rhinos were killed for their horns in a nature reserve in the North West at the weekend.
Altogether 210 rhinos have been killed for their horns since the start of the year, compared to 122 poached last year.
Naidoo said the police's specialist unit, the Hawks, conducted the investigation and made the arrests in co-operation with the Civil Aviation Authority (CAA), SANParks, the department of nature conservation and the national prosecuting authority (NPA).
Farmers in Limpopo's Lephalale and Vaalwater areas, as well as the North West, have recently complained about helicopters with obscured registrations flying over game farms.
The CAA was approached to take part in the investigation.
It was alleged that poachers were dropped on farms by helicopter and then picked up again once they had cut off the animals' horns.
Beeld has heard that the vets from Modimolle have been under investigation for the last few months.
The news of their arrest spread through town like a wildfire on Monday.
Monday's arrests came about a week after Tom Fourie, a well-known figure in wildlife circles in Musina, was arrested. He has already appeared in court and was released on R2 000 bail.
It is not clear whether Fourie is involved with the same syndicate.
Naidoo said the police have their eye on other syndicates that are involved in "the cold-blooded slaughter" of rhinos in nature reserves and game farms.
The investigating team is still searching various properties.
Naidoo said the nine suspects are being held in the police cells in Musina. They will appear in the magistrate's court on Wednesday, at which time the exact charges will be announced.
Faan Coetzee, head of the Endangered Wildlife Trust (EWT), was overjoyed about the news on Monday.
"We've been waiting a long time for this," he said.