SOme do some dont. A while back there was a product that had just this in mind. they gave youa term loan, and a line of credit attached. You still make a repayment, however the Line of credit is drawn to make up the shortfall. It was good for negative geared investors, and Owner occupied wanting a repayment holiday for some reason.
theres also Bill Zheng's mortgage products, which had a similar outcome.
All lenders will certainly want you to show either lo doc or full doc that you can support the repayments without having to use a line of credit to top up the repayments. However if you can qualify for the loan, and you would just like a small line of credit for future investment purposes, thats fine.
You might just happen to use the line of credit to help with property holding costs later on.