Does ISY 994 firware 4.7.3 support GE Jasco switch?  I can't get it to link in Z-wave no matter how close it is to the ISY.

Yes - worked fine for me.  Note that you may need to exclude the device first, before you can include it into the ISY.  You can do that in the ISY - just select the "exclude" menu option, and then do whatever it is that's required on the switch to enroll it.

I believe at least one of my switches is this (from Lowes?).  Worked fine for me.

I bought five Jasco plug-in modules, and four Leviton, at the same time. The Leviton units all paired the first time without issue. ONE of the Jasco units paired the first time, while all the others had to have the pairing button pressed repeatedly - one of them more than 20 times - before they paired. I tested this with both ISY and Homeseer controllers, and in all cases well within range of the controller (2-5 feet away in two cases). The units all work reliably once paired based on 1-2 weeks of modest use, but I can tell you that I’ve purchased my last Jasco products. The Levitons are clunky and I don’t like the placement of the on/off/pair button, but they appear to be rock solid based on limited testing and comparison.