An example being:
"The chain of kindness begins with donations from individuals, foundations and businesses who (or that) truly believe in our mandate and mission."
You can use either who or that, as you wish. That's the rule for a restrictive relative, which this is. There's no difference in meaning, and both options are completely grammatical. Got all that?
That said, however, since this is being done to compliment the people and groups contributing, probably using who will help humanize the foundations and businesses. This is complimentary.
Another thing that might help along that line would be an Oxford comma after foundations, which would put foundations and businesses — each — on the same footing as individuals, instead of being separated out into their own nonhuman category.