I'll leave it for others to cite equivalent references in other States but the Australian words, from the AIP, are -
10.5 Aircraft Performance
10.5.1 SIDs provide specific aircraft performance parameters. The design climb gradients shown are provided to assist the pilot in maintaining obstacle clearance.
In respect to speed, the only rational interpretation is
(a) the relevant measure is geometric gradient - with reference to the hard bits for which ground speed is relevant. The calculations are made with reference to ground speed.
(b) the pilot may not have a convenient reference to ground speed (although that is becoming ancient history with the increased use of satellite navigation) so documentation can be expected to refer to ground speed corrected to IAS, for which the pilot invariably has a cockpit reference ie when the plate refers to IAS, it really is talking about GS corrected to IAS in a conservative manner for convenient operational use.