First of all, what are the details of what kind of a "donation" you are talking about?
I don't think you have to worry about losing your tax exempt status, (there is no tax deduction involved if you are filing an 1120H), but generally, this is not a good policy as I doubt it is permitted under your by-laws. Homeowners expect their fees to be used in connection with the operation of the association, not for some other purpose that the Trustees or Board wants to use it for.
If I was your CPA, advising you I would say not to do it. If certain members want to make a combined donation to a specific not-for-profit, you should have them wrtie their own checks to the organization and send them all along with a note to the orgainization that simply says you made a collection for a contribution to them & enclosed please find the individual contributions.
to this method: 1) Each individual member would be entitiled to a tax deduction for their contribution & 2) It keeps you're Homeowners Association out of the picture, which eliminates any potential issues down the road if anyone were to object to what you have done.
So basically, I agree with your Treasurer, but for a different reason. The IRS isn't going to get involved in something like that, but you have more of a potential problem with any individual homeowner that either objects to that or gets disgreunteled over something else & uses that donation as a way to cause trouble.
It's like a family where everything is OK 99% of the time & then something happens which results in a problem where none should exist.