Yes, as long as you actually withdraw the money from the Roth IRA (take a distribution) and don't try and do a rollover or direct transfer.
If you take a withdrawal, and follow all the usual rules for withdrawals, then once the money is in your bank account, it becomes the same as all your other money and you can do anything you want with it, including putting the money into the pre-tax IRA to offset the loan amount. (Note that this is not a "contribution" to the IRA and should not be done in the normal way. It's technically a special type of rollover from the 401k to the IRA, and the IRA trustee should require special paperwork to process this.)
