I just tried this under Windows 7 with Quartus 15.0 Modelsim 10.3d. I started a NIOS II IDE shell first, used 'which vsim' to confirm I was going to run the correct version of Modelsim, and then ran 'vsim', without the -gui option. The Modelsim GUI console output was:
The first "Hello!" was printed on the NIOS II IDE shell command-line.
ModelSim> puts "Hello!"
ModelSim> echo "Hello!"
Adding the -gui option redirects the output to the GUI console.
Thanks for posting your solution, it works great!