My friends mother died and owns a business and property. He wants to put me on his moms payroll so that I can cash a check to pay bills is this legal?

I'm not entirely following what the accountant is proposing, but it doesn't sound right at all.  Who is the "they" who will right checks to "them" and "they" can cash the checks and give the money back to your friend?  The "theys" and "thems" are totally unclear. Why would anyone need to write a check to a business to have the business cash it and then have the cash given back?  Also, if your friend is not the person who the will bequeaths the business and the house to, who is, and why is your friend medling in that person's inheritance?  Your friend's mother's estate should be in probate and an executor should be appointed who should be taking care of these bills and expenses, and running the business until the debts of the estate are paid and the assets are distributed to whomever the will says.

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You should not pretend to be an employee if you are not in fact working for that company, and you should not cash any checks unless the checks are truly made out to you as payments for the work you have performed.  As the other attorney properly points out, you may incur tax liability for receiving and cashing these checks.  There are also various legal issues with what you are describing.  Your friend should consult a probate attorney to see whether the estate of his mother will be able to pay the mortgage on his late mother's house. 

I recommend you and your friend each consult your own attorneys.

You're not getting any personal benefit out of this, which is likely to be helpful if there's a problem.  But I'm a bit surprised to hear that the accountant suggested this, because there are a number of potential problems here, mostly for your friend.  I'd suggest that you get written receipts for the money involved, for one thing, to prove that you aren't profiting here.  I'd also suggest that you talk to your own accountant or tax professional, because you may have to report this on your tax return as income, even though you didn't end up with the money, and that could cause you additional tax liability.