Was an employee (and am a happy equity-owner in Asana as a result), and I wouldn't be worried about that - I trust the Asana leadership to ensure clean terms with the investment.
If anything, I'd worry about the anchoring effect - e.g. if the SaaS valuations decline a year from now so that a prospective Asana IPO wouldn't be worth much more than $1.5B, would that result in them being more reluctant to IPO?
But that's the effect that is plaguing unicorn startups - the ones that have to go IPO or get acquired at less than valuation see the employees getting pennies on the dollar for their equity, while the investors that gave the startup the unicorn status take the bulk of the pay out.
Do you know the terms of this latest round of funding? Has senior management confirmed the class of equity?
I'm not a current employee, and even if I were, I'm not sure that would be something I could disclose. But I can tell you that in the past Asana leadership has been very good about insisting on clean-sheet terms for investor funding.