I'm hoping to pair a Shimano XT cassette (11-42) and an Ultegra crank (50-34t). Would this work for a Soma Wolverine v2.1 (someone mentioned this wouldn't do for "road cranks on mountain bikes") ?
The Wolverine is a road bike (or 'monster cross') not a MTB. The Soma web site says that the rear spacing is 135mm, I assume the BB shell width is 68mm. If that is the case you can run a Shimano road crank and road chain-line.
Compatibility between the crank and cassette is not what you need to deal with. Presumably you are either thinking of installing an MTB drive-train with an Ultegra crank, or a road drive-train with a MTB 11-42 cassette.
An MTB front derailleur will have trouble with a road 50-34 crank. Most road derailleurs will not handle a 11-42 cassette.