Interestingly, the installer--despite having the appropriate Voodoo kexts--insisted upon having both a USB mouse & keyboard; none of the integrated HID devices were recognized. This is not insurmountable, as external peripherals can be attached. It was also an incredibly, nightmarishly slow process just to boot into the installer. I did find that even without an external keyboard attached that, if I had a USB mouse plugged in, if I clicked fast enough it continue through the installer without a keyboard present.
I should back up just a bit here; I partitioned a thumb drive according to RehabMan's guide, having an EFI partition with the latest Cover installed. For my installer, I downloaded the latest macOS Mojave from Apple and used the patcher provided by dosdude1. I did this because my Intel HD3000 graphics are not natively supported in Mojave. Additionally, I copied relevant kexts from my live EFI boot partition to the EFI partition on my thumb drive; essentially creating an installer customized for my particular model ProBook.
My experience is that 10.14.5 is much smoother and more stable than 10.14.4 (was experiencing random lockups). Everything seems to work properly now.
Caveat: I'm installing the full update because I've elected to keep my drive as HFS+, rather than convert to APFS. Your mileage may vary.