"Singlets"???Hawthorn have history with white number panels on their singlets. They had it when they won their first 2 premierships, and reintroduced in 2008 which coincided with beginning of the most recent premiership era. Given it's a 'legends' singlet commemorating Peter Hudson, the club thought it was appropriate to include it as it was a feature of the singlet during his time at the club.
I doubt the Port Adelaide design was considered at all. Overall it really didn't cause an issue between telling the two match-day teams apart.