Epidemius' 'The sands of sickness' item does not charge the Nurgle army abilities. I ran a test with four plaguebearers fighting four longbeards and after 3 minutes they generated around 50 tickets for the army ability.

I ran the exact same test again, this time using the Sands of Sickness as soon as the units got into melee. The number of tickets was roughly the same, around 50.