For every type of business entity other than an S corp or an LLC electing to be taxed as one, the IRS either doesn't care about any notion of reasonable salary or - in the case of a C corp or an LLC electing to be taxed as one - actually wants it to be as low as possible (whereas the owner wants to maximize it).
You can't have it be 'insignificant' salary but you can do plenty of fringe benefits or long term profiteering via acquisition as mentioned.
I will say, ironically, the small business owners like that were great to work for, although they were paranoid, they were often generous to employees.
OTOH, at the computer shop there was a standing rule that if the CPA brought his computer in it was 100% priority and we treated him better than the one org that was 10-30% (depending on year) of our entire gross income...
EDIT: To be clear, it's complicated, https://news.ycombinator.com/item?id=42199534 is a good explanation of where I sit overall.
That still seems like heavy handed overreach to me. Should they not instead contact you for clarifications about the ambiguity?
How many times were you audited before learning this valuable lesson?
You hear a lot of anecdotes both ways and it is quite hard to get a good picture of the real situation.