There are a lot of historical UDFA college guy success stories, but many of those are also quite old, from the time where the NCAA in general was underutilized as a source of prospects and more guys were likely to be ignored.
Back in the day you had the likes of Adam Oates, The-Goalie-Who-Shall-Not-Be-Named (BOOOO!!!), Brian Rafalski, Curtis Joseph. Slightly more recently came the wave of Dan Boyle, Marty St. Louis, and a couple others that are either less impressive (Tyler Bozak? The Tanev brothers? Matt Read?) or who I just flat out can't remember. And Torey Krug as the outlier recent big success.
But in the last 10 or so years the "best unsigned guy in college" hype train has picked up. He wasn't UDFA, but I feel like this started with Justin Schultz spurning the Ducks and people going nuts over him. And since then it always feels like there's this coveted top-shelf "everyone will want to sign this guy" player that's highlighted every year and most of the time it amounts to nothing.
Here's a list from 2013 that was tracking signed UDFA (or at least unsigned FAs including graduates spurning their draft team):
The list is, I tihnk, chronological but I distinctly remember that the #1 guy on College FA ranking boards was Danny DeKeyser. He was alright for a couple of years then regressed to being an acceptable depth guy. Also note that the same list included praise for the Sharks signing Troy Grosenick, Eraiah Hayes, and Rylan Schwartz. And we know how that turned out
Outside of Nate Schmidt and sort of DeKeyser, that whole list is a big fat load of nothing or "slightly better than nothing"
Here's that same blog's 2014 list:
This is a less glittering list than even the previous one because there's Trevor van Riemsdyk and then honestly #2 might be Ryan Carpenter by the Sharks.
Here's a 2015 list in 3 parts from Last Word on Sports because the previous blog either stopped doing this list or I just can't find it (and the seems to have died in 2019)
What do we have to work with here? Drake Caggiula? Evan Rodrigues? What a murderer's row.
LWOS 2016 list:
Top 2016 College Hockey Free Agents
Still Drake Caggiula because I guess he didn't sign the year before. Matt Grzelcyk, Troy Stetcher, Alex Lyon...
Obviously there are legit NHL players in here and getting a guy who's even halfway useful without spending a draft pick is a win. But if we're supposed to hold our breath on drafted prospects because of the unlikeliness of them succeeding then UDFA college guys are probably going to require you to hold until you turn purple and pass out.
Just thought I'd bring things down because that's what it's like to be a Sharks fan right now