[SNIP] Information on how to share my work in IDA without putting myself out on a limb legally *very* welcome. [SNIP]
I'll admit that I haven't used IDA (but I am aware of what it is and what it does).
I am not an IP lawyer, but what about distributing the delta between your commented, reverse engineered IDA file and a plain IDA file of the firmware that anyone can easily produce from their own 'scope?
That way you would not be distributing Rigol's copyrighted code, merely a file which contains your comments etc and (machine readable) information on where to insert it into a locally generated file which already contains Rigol's code. Persons using your diff would of course have to obtain their own dump of the same firmware version that you used.
Another approach (which works for people without IDA licenses) is to distribute a symbol table of memory addresses and what you think they are used for (variables, subroutines, interrupt handlers, etc), which someone can then use to understand locally produced disassembly of the copyrighted code (again, you do not distribute Rigol's code, just a list of what addresses do what).