Can you use red lotus to negate Darkness Blades E?

yup

by playing DB E: you just played an ability that allow you to commit your opponent cards.

Cass said:

I wasnt sure how that would work since the ability isn't (at the time it is played) commiting anything.

Thanks

Yes you can negate it with red lotus.

Stampage. The ability may (eventually) result in cards being committed so you can respond to it, similar to Chain Throw's Enhance.