In the current version of SAM 6.x, is the label display above the chart limited to showing only 30?
The Multiple Object Chart is not limited to 30 data series in the chart, though as you can see below 30 is quite noisy as it is. 45 would only make it worse. The chart on the left shows only 30, while the one on the right shows 45 (yikes). Note the legend table is limited to the first 30 entries.
If so, is the actual data from all 45 servers represented in the chart?
Yes, though it's likely difficult to decipher when there are that may series represented in a single chart.
If so, is it possible to change this?
The legend table is limited to 30 series and cannot be exceeded.
Would it be possible to have a single MOC that contained data displayed individually from multiple resources, but NOT show the labels (takes up valuable space), and allowed you to view the source by hovering over the data points / lines?
Yes and no. The new Custom Chart resource in SAM 6.1 does provide the hover with more information. However, this resource is limited to 10 data series in the chart by default. This can however be adjusted under [Settings - Web Console Settings] to show all 45 in the chart as well as the legend table.