Graham, yes you can, as the museum is situated in a kind of plaza that does not require purchase of a ticket unless you are going to the indoor museum proper. I'm not sure how it works if the museum is actually closed as they might close the gate from the street. If it was closed you should still be...
Outdoors at the MAXXI Museum on Via Guido Reni in Rome is this G91 (inverted, unfortunately). It's outside the museum building (at the back) so no entrance fee required. MM54416 Fiat G91T/1 by Irish251, on Flickr
I don't think so, as I saw and photographed it on the ground and being pre-flighted about an hour later (1730 local) - unless it had flown in the meantime?
At about 1600-1630 on the 6th (Saturday) an ALAT helicopter was noted departing to the north. It may have taken off from the ramp area to the east which was inaccessible to the public. It looked like a Gazelle but I haven't seen one listed. Any ideas?