Yes, several members noticed for sure. We can clearly see Ty Longley and the bass player looking up at it in the last couple seconds before Brian Butler moves away from the stage, and in his grand jury testimony the drummer mentions it as well:
"I looked at it and I was, like holy shit, but um, I thought it was pretty small at the time, it was right off the bat I thought somebody was gonna to come up to put it out, I didn't think there'd be a problem, so I didn't want to - it concerned me but I didn't want to stop playing and get bitched out, like what the hell are you doing stopping the show and, that was my main thought, but then it start - nobody came up, it started gettin' bigger and then I saw Dan run up and try to throw water ... I saw, you know, the flame was just rapidly growing. I was like that isn't gonna do shit. I stopped playing before anybody in the band and I, and I ran out. Well, I got out of the cove and by the time I turned around that flame was up on, over the, getting over the ceiling, onto the ceiling and I heard the security guard, I didn't see him, but I heard him say, get the fuck out of here."
If Jack Russell did notice, it probably wasn't until fairly late. He obviously doesn't see it when he's on camera and seems oblivious to the several fans near the front that start pointing and waving and yelling just before Butler moves away, and in
this picture which Adam Florio took several seconds after Butler moved away, Jack Russell and Mark Kendall are still seemingly oblivious to it.
As far as making an announcement goes, it surely would've helped a lot. However, I would personally put that responsibility on the security staff rather than Jack or anyone in the band. I doubt most musicians at any given show in a random city have any serious knowledge of the venue layout or how to initiate an evacuation, etc. They're just there to entertain people for the evening, anything safety/security related should be handled by appropriately trained venue staff... and of course that was just one of the countless shortcomings of the Station and its management.