For whatever reason, it "feels" better when it's written out, rather than the symbols. It's been like that for years, but the advisor is right: there really is no difference.
In NPHC orgs, we don't typically have event shirts and really try not to appear on all-greek t-shirts unless it makes us look terrible that we haven't included ourselves.
It really comes down to the individual policy of your organization, though. If the org is silent on the matter, then local practice rules. And yes, that varies by campus.
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