How to achieve common ground for a single ended input?
Figure 5 is really saying that having two grounds on the system can cause problems. Those that do have two seperate grounds are fed into differential amplifiers which effectively circumvent the problem of multiple grounds.

Figure 5 has two columns and the diagram that has the cross through it is in the column marked "ground referenced signal sources". If your measurement device has galvanically isolated signals from it's metal casing (if it has a metal case) then there should be no problem - it falls under the column marked "floating signal sources".