Corporate jet Captain reported VNY Clearance Delivery issued a departure clearance that was confusing to follow with the verbiage of the SID due to a crossing restriction.

Narrative

This is intended as a hazard report regarding a possible future safety problem due to non-standard phraseology included in a CPDLC DCL (Departure Clearance) at VNY. Premise: There is an important fundamental difference in an IFR clearance to either climb via SID except maintain 4000 ft.' and/or 'climb and maintain 4000 ft.' That day our clearance was WLKKR4 RNAV SID and maintain 4000 ft.; which to me means an unrestricted climb to 4000 ft. But the SID includes a crossing restriction at or below 1750 ft. at 1.5 DME; which our Aircraft X could easily exceed that day. I used voice to contact Clearance Delivery for clarification and express my concern. He said that the 1750 ft. at or below restriction still applies. I was surprised and politely said that other airports may have issued 'climb via SID except maintain 4000.' He understood my concern and question; but said that that is the way they have been issuing the clearance at VNY for the last few years. So therefore; obviously we complied with the at/below 1750 ft. restriction during the initial climb. In my opinion; this is non-standard phraseology for ATC's expectation. As a supporting example; I have departed OAK with similar SID at or below restrictions during a very low traffic period and was cleared to climb and maintain XXXX ft. When I asked for confirmation of my unrestricted climb clearance; I was told yes the clearance was for an unrestricted climb."