Interesting topic! Much can be said about this. In some countries, this external financial support is working since very long time ago while in other countries only very recently have been introduced. I believe this happens also due to political will, and not only because of the museum decision. It is always a positive thing once the collection conservation is assured.
In case the museum is accommodating "corporate events" it does not imply necessarily that the museum will receive more visitors, especially if they do it for financial need. For example, there are museums that are renting their gardens or some conference rooms that are apart/independent from the visitor circuit. Not very long time ago I went to a conference in the Hermitage and it was in a part completely independent from the main building, with its own entrance and everything. Of course in the last day we could go to visit the museum but we were so few when compared. I have also been in others where the conference is only held in the museum but there is no visit included, also because the schedule may not fit with the normal opening of the museum.
In case the museum is hosting some events that will increase significantly the number of visitors, of course it has to be certified that the increase of the visitors will not have a negative effect over the collections. I'm hoping the museums have always this concern. However, it always depends from which kind of collection is and the number of visitors. Were you having in mind a specific case?

Apart from the changes of RH and temperature levels that will occur in the case of the gathering of large numbers of visitors in the museum, another subject that arises is the 'quality' (if I may say so) of the visitors. What I mean by that, is that people who choose to visit a museum in order to admire its exhibits, are more or less sensitised on the subject and they will treat the exhibits with respect. Does the same thing occur when people enter a museum in order to attend a party?
 
Last summer, the Museum of Natural History Museum of the Lesvos Petrified Forest, organised the "Volcano festival", which included a video-art temporary exhibition and an alternative punk-rock concert with three bands from Athens (there is a small stone-built amphitheatre in the museum yard, constructed to host various cultural events). A lot of young people came in the museum for the concert; people who I do not personally believe that would normally bother going to a museum. At the night of the concert the exhibition rooms were closed, but the people who attended the concert could see some of the petrified tree-trunks that are located in the museum yard. It was nice to have all these young punk-rockers in the museum. They may had come just for the music, but they also took a look at some of the fossils as well, and some of them were actually thrilled. However, during the party, the museum staff had to keep reminding the people not to touch the fossils, not to sit on the long petrified trunk that was in front of the amphitheatre, not to leave their bags and booze on the fossils, not to smoke next to the fossils, not to.... blah, blah blah, blah.... Luckily both the fossils and our ears survived the alternative punk-rock concert and in the end everyone was happy!