It depends on what your definition of "allow" is. Reminds me of an impeachment hearing discussing the definition of "is". Anyway, the IRS Direct Pay website requires the taxpayer to go through a page of identity questions, questions you and I can answer on behalf of the taxpayer (what was your address for one of your previous 5 tax returns, for example).
I've sat with a client (over the phone) and whilst in my office, going through the screen prompts on IRS Direct Pay and the IRS never knew it was merely me punching in several key strokes.
It's a good question. I've never tried to enter my account number, or an account number belonging to someone other than the taxpayer, but I would forge a guess (shot in the dark here), and say, no, it doesn't matter what account belongs to whom. As long as there are funds available, the IRS will come a-snatching-away of the funds from said account.
But, having not ever paid an IRS debt on behalf of a client, I cannot say for certain. However, I did stay at a Holiday Inn Express last night, so.....