"Official" Answer is no, but I do not understand, why not -;(
To find answers of this type (supported optics/cables/etc.) use:
1. Go to Juniper Support - https://www.juniper.net/customers/support/
2. Select Documentation & Tools -> Pathfinder (https://pathfinder.juniper.net/home/)
3. Select Hardware Compatiabilty Tool (https://pathfinder.juniper.net/hct/category/)
you can then search by exact hardware sku or model type. If you use SKU will eventaully bring you to:
https://pathfinder.juniper.net/hct/model/?component=EX-QSFP-40GE-DAC-50CM&tab=sPlatforms
where EX4600 is NOT listed, but QFX5100 is. Since these 2 products are basically the same HW, not sure why listed as supported on one, and not on the other???
If you search by product, should land you here - https://pathfinder.juniper.net/hct/product/#prd=EX4600, which again does not list the 50cm length cable.
Good luck.