Santos said he had recently been threatened at his home by a large man wielding an axe so wanted protection in case he'd returned.
Santos and the dogs went in through the back door and into the kitchen where Nowacki was setting up his meth-testing equipment and he held the door closed as the animals attacked.
Nowacki was bitten three times and tried to escape through the kitchen windows.
HNZ chief executive Andrew McKenzie told the Herald after the incident last year that Nowacki received "pretty severe wounds" to his legs, hands and forearms and was in hospital for several days.
Santos admitted causing injury by way of the dogs but disputed he had reckless disregard for another's safety.
Judge Evangelos Thomas said Santos made no attempts to find out who was in the house and knew Housing New Zealand were due to visit for the testing.
"Sure, there were other possibilities but it was just as likely to be Housing New Zealand as it was to be anyone else.
He also could have prevented the dogs from going into the kitchen and he considered that was "unreasonable under the circumstances".
Judge Thomas convicted Santos on both charges and remanded him on bail until sentencing in November.
The dogs were put down after the attack.
