Yes, it can:
Standard RAM:32 GBMaximum RAM:128 GB*
Details:*Apple reports that this iMac Pro supports "up to 128 GB of quad-channel 2666 MHz DDR4 ECC memory." By default, it ships with four 8 GB memory modules. At the time of purchase, Apple also offers to configure this model with 64 GB or 128 GB of RAM for an extra US$800 or US$2400, respectively.
Here are the kits available from OWC to do a RAM upgrade:
https://eshop.macsales.com/upgrades/apple-imac-pro-10-core-late-2017-3.0-ghz/memory