Short answer: partly, and you should be careful with the partly.
The appeal is obvious. If your line of credit has room in it, that room can absorb a busted furnace the same way a savings account can. And unlike the savings account, money parked in the line is cutting your interest bill while it waits for trouble. Idle cash earning less in savings than the line charges in interest is a dollar doing half its job. So yes, once the strategy is running, the line really is a layer of your emergency plan.
Available credit is not cash, and the difference shows up at the worst possible times. A lender can freeze or reduce a line, and the classic trigger is exactly the kind of economic stress that also threatens jobs and home values. It happened to plenty of HELOC holders in 2008 and 2009. Cash in your own account can't be revoked by a nervous bank.
So the sturdy structure is layered. Keep a real cash buffer, smaller than the old three-to-six months if you like, but real, in an account nobody can pull back. Let the line stand behind it as the second layer for the big, rare stuff. How thick each layer should be depends on your income. Commission and self-employment income need more cash floor than a steady salary does.
And keep the cushion rule sacred. Room in the line only helps if the room exists, which is the whole argument of The Rule That Keeps Parking Safe: Never Max the Line. A maxed line can't rescue anyone. At that point it's just debt. If you're setting up your layers now, the How It Works page covers the order of moves, and the broader safety-net questions live at Oregon Cash Flow Pro.