Hi John !
Ukemi means something like "recieving the technique" so it is much more than rolling/
To help nage/tori perform the technique
uke must provide a good quality attack that
is needed for the technique to work.
Good ukemi is neither forced nor weak ,
good ukemi makes Aikido real , but still it is a work of cooperation even at the highest speeds.
So calling ukemiwaza atemiwaza ,is probably not far off.