I didn't see anything that felt like cheating, but this might be a subjective issue. The way I see it, the housing allowance is part of the compensation. If the minister can move the home equity into some sort of investment(s), or build a fence, in order to make full use of the housing allowance, I don't see that as unethical. It seems like from the original post that the allowance has rules about what counts toward the benefit.
+1
I'm also a minister (Anglican, in Canada - equivalent to Episcopal in the U.S.).
Our compensation package is broken into two parts - stipend, and housing. The stipend is relatively low, because the value of the provided housing (a rectory to live in, or a housing allowance) is quite high. Each parish is supposed to have available a rectory, and that rectory has to meet certain criteria in terms of # of bedrooms, etc. This means that parishes won't need to choose their minister based on size of family, or ministers choose based on size of house. However, there's been a shift, and more clergy are wanting to get into the housing market, so they don't retire with no place to live. So even if a parish has a rectory, the minister can negotiate to get a housing allowance instead, in which case the parish tends to rent out the rectory to compensate. I chose that route, and am renting my own place that is a better fit for my situation. But even if I did purchase my house, I would still be entitled to the housing allowance after my mortgage was paid off, because it's part of my compensation package.
Also, I wasn't clear if the OP was asking about the housing allowance received from the church, or about tax deductions?
The housing allowance portion of my compensation is un-taxed, up to a certain percentage of my total salary. Being credentialed is not the only criteria to receive this benefit, you have to be working in and responsible for the care of a parish, and I receive a letter from my Diocese each year to provide to Revenue Canada, confirming this is the case. Assistant clergy, as long as they are in parish ministry, are also eligible. As I don't own a home, I'm not sure what happens if I don't have the offsetting expenses, or what offsetting expenses are allowed in the view of Revenue Canada. I will look forward to finding that out some day!