Vega FEs are allergic to 18.3.4 and I'll get less hash-rate on Alloy/Heavy and CN7, on Alloy there is alot of STALE shares too, so the only viable driver is 18.6.1.

Results for a rig having 5 Vega FEs SRB Miner 1.6.4:
driver 18.6.1
CN7  = 11060 H/s
Alloy = 5670 H/s
note: Mining Alloy, on DevFee we get miner crash or error

driver 18.3.4
CN7  = 10900 H/s
Alloy = 5580 H/s
note: Mining Alloy, there is a lot of STALE shares.

Results for a rig having 5 Vega FEs SRB Miner 1.6.1:
driver 18.6.1
CN7  = 10910 H/s
Alloy = 5630 H/s

driver Blockchain Aug 23
CN7  = 10910 H/s
Alloy = 5630 H/s

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So in conclusion:
18.3.4 won't work for Vega FEs. For Alloy we have to use 1.6.1 and we get similar hashrates as blockchain driver.

Edited: The said crash/error occurs not on DevFee but right after when resuming!