I was mostly considering the Dream lens I have for the 7 but It looks too big and bulky probabably so instead was considering the smaller yet longer 135. Anyone got rolleis into concerts before?
I have certainly shot at concerts with a Rolleiflex, but in those cases I, personally, had investigated in advance and ascertained that it was unlikely to be a problem. So that answers your question but is probably not much help.
One thing I always do is to do my homework ahead (of course you're doing this to an extent, now, by asking etc). But this venue (the arena?) should have a website. The concert promoters/ticket sellers should have a website. First up: take a look over these and see what you can find about precisely what is or isn't permitted in terms of cameras and photography. This information may or may not be easy to find, and may be a part of the ticket sales "terms and conditions" or "conditions of entry". Once you've referenced that you may have a better idea of whether anything is allowed at all and, if so, what.
Eg (I'm in Australia) and on a visit to an AFL game a few years ago nearly got refused entry to the oval by security. No professional cameras, they said. I was toting a 35mm EOS and Konica RF (I think). But I'd checked the venue website carefully beforehand, and politely pointed out to them that, there was absolutely no mention, on it, of a ban on camera equipment. That, and the fact I was using film, not digital (nobody uses film professionally these days, was my stance--I may burn in photo hell for my sins). They relented and let me in.
So: do some research: if answers are not forthcoming, email the promoters for more information. Explain your situation, frankly. If they advise in the affirmative that a Rollei/35mm RF/SLR is not a problem--print this and take it with you. If the condition is Eg: 'no SLRs"--either your RF or TLR should be OK. If it's "no interchangeable lens cameras" your Rolleicord is a perfectly legitimate candidate (I always fancied my Tele Rolleiflex because of this, for obvious reasons).
Worst case scenario it is going to save you pointlessly lugging a camera along that is not going to be passed through security, but the more information you have on hand, the better equipped you are going to be.
Of course if you know the artist this always helps. I've been able to shoot a few times simply by either knowing the artist, or, contacting them ahead of time and asking them, politely, if I could get some shots. But the bigger the act the more impossible it tends to be, to be able to actually reach the artist, of course, so...these things are not always possible.
Cheers
Brett