I think the club will need as much income as they can get when the game resumes.
Would be better offering deals for season tickets for remaining games and/or for the first game. That would generate some immediate income for the club if it was taken up. If the season was subsequently abandoned, tickets/season tickets could be used next season.
Rather than turning up dressed as nurses etc, why not promote the sale of replica tops, so that Widnes fans will turn up in Widnes gear. This would also generate some immediate income.
You could still show appreciation for NHS staff and all other key workers who have been working during the crisis, as well as the volunteers. Maybe by inviting representatives from these groups to a VIP event at the ground and invite them on to the pitch pre-game for a deserved round of applause.
This would not prevent those with a wish to dress as a nurse, to do so.