Echoing what Lugia and others are saying, why use a Eurorack rig for live hiphop instead of one of the "grooveboxes" like Tempest, Elektron Rytm, Maschine, or one of the MPC line?
A few questions I'd recommend considering (if you haven't already):
-- what's your preferred workflow for playing / programming beats? (e.g. rack sequencer, outboard sequencer, finger-drumming, etc.)? There's really a huge difference in workflow for different setups; I find some of the sonically appealing rhythm rigs have a painful (to me) workflow.
-- what are the desired core sounds? What platforms help you get those efficiently?
-- what sound polishing / fx / mixing are needed to get the final audio? Things like MPCs and Maschine are built to get you performance-ready sounds, volume leveling, bus compression etc. Other rigs, it may take more thought / work / additional modules to get the same "performance ready" sound.
IMO, MPCs are great rigs for hiphop: they're proven over decades of use, and they've really refined the platform specifically for hiphop. Maschine is also strong for that genre.
IF you're really committed to doing hiphop with Eurorack THEN I suggest really zeroing in on a sequencer you're going to love to work with. If you'll be happy working with the combo of Hermod Sampler and OP-1 (which you mentioned above) then that's cool, I just want to emphasize that the sequencer / interface will be key to having fun and getting good results. If I was building a Eurorack rig for rhythm, I would use Erica Synths Drum Sequencer, which is the best small format sequencer I've ever spent time with, OR a stand-alone sequencers to send MIDI in such as Polyend Seq 8 or Linnstrument. The standalone sequencer would give more room to work on a sequence grid AND free up HP from your rig. As far as reference Eurorack rhythm systems go, IMO Erica Synths Techno system is a very good implementation of the "groovebox" concept, BUT it retails near $5k and it voiced more towards Techno vs hiphop.
All considered, I'd urge you to see if a MPC will work for you, and if you really want to do Eurorack, focus on making sure you have a sequencer setup you'll love to work with.
Good luck!