Carter had a "lengthy chat" with Keenan yesterday and said he had received a character reference about Keenan, which was very supportive of him.
He had no qualms about Keenan taking part in the Tauranga International Marathon.
"Our position is pretty simple and pretty clear," Carter said.
"He's welcome to participate in our events."
He said none of the Total Sport events were sanctioned under Athletics New Zealand and his business was about running inclusive events for people of all abilities, and they did not have any immediate plans to change things for the future.
Carter said he was confident in Keenan's explanation for what he did.
"I... think he maybe made a naive decision," Carter said.
Keenan had previously admitted he had ordered and paid for Erythropoietin (EPO) online from an overseas website and submitted a letter saying this was to address a medical condition and not for performance enhancement.
EPO is listed as a prescription medicine and is prohibited underclass S2 peptide hormones, growth factors, related substances and mimetics on the 2017 prohibited list.
His suspension period of four years was ordered by the Sports Tribunal of New Zealand.
The parcel was intercepted by New Zealand Customs and referred to Medsafe which advised Drug-Free Sport New Zealand. Following an investigation and communication with Keenan, the product was destroyed.
"It's an unfortunate incident, and it's cost him an awful lot," Carter said.
Athletics New Zealand chief executive Hamish Grey said Keenan being able to compete in the Tauranga International Marathon was in his opinion "frustrating" and unfair to other participants.
He said although the Tauranga International Marathon was not classed as an elite event he believed if they applied the same rules every participant would benefit.
He said in his view it was "disappointing" the event and the sport was "brought into the headlines for the wrong reasons" because of one person's actions.
Drug-Free Sport chief executive Nick Paterson said "rules are the rules" and Keenan had not broken any, but it would be good to have some consistency over the issue.
He said the issue wasn't with the event itself or Keenan, but it would be "good to have consistency" when it came to drug bans.
He said his concern was for the other athletes and how they felt knowing someone who had been banned from other events was able to compete against them.
A total of 1300 people entered the nine events offered as part of the Tauranga International Marathon with running and walking options in the marathon, half-marathon, 12km and 6km distances as well as a 1.5km Superhero Kid's Dash for children under 13.
A total of 1074 people completed them.
