Neat topic. Hardly any books cover the topic of rather to disclose to co-workers and others your REI activities.
I went sort of yes, no, yes on it...
And it may depend on your context (type of work and the demographic and psychographic of co-workers).
First, if you work for some employers you may have to disclose it. Like my day job with a subdivision of the state, I disclose all business dealings.
So it was not top secret for me anyhow. Never been an problem--just a formality (I just note I do REI on my own time, with my own resources, and it is unrelated to my job duties). There is just a conflict of interest form to sign with my annual contract. Check with your hr dept if you are unsure.
Second, more on the social and psychological level where I think the question aims--it may depend.
I housed someone that worked in the same organization early on, so word got out. I didn't really mind, but in my context (a college) some folks are not as keen on free market capitalism in general....
With just one mid-level condo housing a professional at market rates--someone called me a "slum lord" and another said I was "a capitalist" (the latter of which I think they meant as derogatory--but I kinda appreciated or preferred to being called socialist or communist).
So I kept it more low key after that. I sensed it could make me vulnerable, like if you misssed work or something, folks could be like "oh, he must be out showing a rental house or something". Or some may paint you as the greedy villain.
But the good news, the cat was out of the bag, and once you have been called a slum lord it is rather liberating.... it can't get much worse.
In fact, it frees you up to not worry about what others think. You see their comments won't be driven by rationality or anything you are doing--but more about someone's insecurity with your ambition or direction. It's them. Not you.
And "yes" your extra motivation and business savvy will be a trigger for some folks. It takes them out of their comfort zone, for with about the same income and time constraints, you acquire and manage a half dozen income producing properties and they binge watch Netflix from an underwater single family or maybe just rent! That an rub some folks the wrong way. But this is much the same as if you do award winning daily work, get a promotion, or author a book....it just makes some folks unhappy. Avoid them.
Finally, you actually may find several folks in your workplace have rentals (be it a vacation rental, an accessory apt or the duplex down the street) or other cool side hustles. And it can even become something of a badge of honor and part of your identity.
I even took what was at first a possible workplace vulnerability and made it a strength. For example, in my job we are encouraged to do writing, so I did a book for the part time landlord and was honored at an author's reception!
So you see the transition from some possibly frowned upon side hustle to getting an award!
Best of luck!