Yup. You can buy a house on margin if you like. With Interactive Brokers' rates as low as 0.75% for large balances it doesn't look like a terrible option vs. an adjustable rate mortgage, if your account balance is high enough that you're not risking a margin call.

If the house is an investment, the margin loan interest may even be tax deductible, without the 750k limit that the mortgage interest deduction has.