JMP has very powerful capabilities in modification and/or the creation of new output displays. For your new request, one only has to add a Spacer Box between the outputs that are being appended.
//nw1 = New Window("vertical tables");
nw2 = New Window( "horizontal tables", <<journal, hlb = H List Box() );
For( i = 1, i <= N Table(), i++,
//hlb << Append(Data Table(i) << new data box); //Active tables on top of eachother
hlb << Append( Data Table( i ) << new data box ); //Active tables side by side
hlb << Append( Spacer Box( Size( 25, 1) ) );
//Data Table(i) << journal; // Journal; tables inactive, for browsing data only
);
Jim