I've found most bandleaders are pretty flexible about it nowadays, if you can play. There was some resistance to it in the early days of EUBs, but most are even okay with my playing the NS BassCello at this point.
I play the real bass whenever possible, because I just flat out play better on it. But I don't think most people will have any qualms about hiring, say, David Friesen because he plays a funny little bass.
Regarding buying a DB vs. an EUB, in my case, it isn't either/or. I play DB, and I own an EUB in order to sound as good as possible for those times when I can't use the real thing. To put it another way, in order of preference for me, it's 1.) My own double bass, 2.) a rental double bass of good quality, and 3.) the EUB.
YMMV.
I am pretty much in agreement with you, but I prefer my double bass first, but prefer my Ergo over amplifying the double bass. The extra strings really help in terms of the give and take.
I would also word it as when the context seems to call for EUB, I use that.
I was in Chicago a couple weeks ago and had my Ergo for a gig but had a recording with a master of subtle chamber jazz, Guilermo Greggorio, so I borrowed a bass. I got the right sound, but I enjoyed playing the EUB the next on a gig much better.
But I do a agree, you are best off having both instruments.