Can they brick the tools by denying firmware updates or something like that?
I don't know for sure but for things like etch or deposition tools the controls aren't that complicated. You can even buy a working controller box on eBay.
As someone who is both in the field (but on the chemistry/materials side) and also tinkers with electronics for fun, I don't see the tools being particularly hard to control on their own, even if you had to make a controller box from scratch with a Raspberry Pi, as long as you knew the pinouts of the cables.
What does an oven, etch or deposition chamber really need?
1. Temperature I/O. You have X channels, usually 1-6, of solid state relay output for heating and equal channels for thermocouple input. Let's call that 2 DB-9 cables: a local serial thermocouple ADC that sends RS232 signals, and 6 solid state relay control signals.
2. Valve open/close. 1 relay channel for each valve. Let's say you have an ALD process. You need at least 2 precursor channels, inert gas purge channel, a vacuum pump valve channel, load lock valve channel. Call it 9 channels to be safe. Controllable via a DB9 cable too.
3. Programming. It's just PID loops. Basically, you have to be able to set a temperature profile (X degrees by X time then hold). For etch or deposition you may need to couple it with a external end point signal like a spectrometer or QCM. That's a bit harder but many of the controllers have programmable end points where they'd send a known signal, like a relay closure at end point, continuous analog data or continuous RS-232 data, to the PLC.
So you can probably buy the controllers directly from 3rd parties or hire an EE (which I am not) to make you a box as a 6 month to 1 year project, as long as you know the pinouts or original cabling.
