Patrick Ryan, who was manager of the centre from 2017 to 2021, also said Ashley was "working towards" a therapeutic model during his tenure but one was never introduced.
The state government is standing by a pledge made last September to close the centre by the end of 2024, despite calls for it to shut immediately.
An inquiry examining child sexual abuse in state institutions has been told the centre has a "culture of brutality" and heard from former detainees alleging they were sexually and physically assaulted by staff.
The inquiry has previously been told a senior worker, known as "Lester", was stood down in November 2020 after historical allegations were raised to Ashley management and the department in early 2020.
Mr Ryan said he became aware of the allegations during the inquiry.
"I'm only aware of the allegations quite broadly, not specifically. Certainly if I was aware of those at the time I wouldn't have encouraged Lester's contact with young people," he said on Wednesday.
"There would have needed to have been some intervention."
Mr Ryan said the allegations were something he should have known about or been advised of.
The inquiry has been told Lester was seen on one occasion strip-searching a detainee in the lead-up to him being stood down, despite a direction that he not be in contact with children.
Mr Ryan said he couldn't recall any instances of such strip searches occurring.
Mr Ryan said when he arrived at Ashley, the centre was "moving to" a therapeutic model.
"There were elements of work being done therapeutically but it hadn't been captured by a process or procedure," he said.
"We were working towards introducing a therapeutic model to Ashley but one was never introduced during my time."
Mr Ryan also said staff training had lapsed when he arrived and a training coordinator position had been left vacant for some months.
Tasmanian Premier Jeremy Rockliff on Tuesday apologised to former detainees who had not been provided with therapeutic care at the centre.
The state government plans to shift to two smaller centres when it closes Ashley.
Mr Rockliff said he understood calls to close the centre, but there were no better alternatives currently available.
Head of youth justice reform at the department of communities, Chris Simcock, said the state government deadline of building two new centres by Ashley's scheduled closure date was "very tight".
"Some colleagues have suggested it might not be possible to achieve that," he said.
The inquiry is holding its final five days of hearings and will hand down a report by May.
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