Yes, both rotating the values and adding a grid is possible with just a few set commands. The following code, modified from Plot a spiral with gnuplot, does both.

use strict; use warnings; use 5.010;
use IO::Handle;
use File::Temp "tempfile";
my($T,$N) = tempfile("plot-XXXXXXXX", "UNLINK", 1);
for my $t (100..500)
        { say $T $t*sin($t*0.1), " ", $t*cos($t*0.1); }
open my $P, "|-", "gnuplot" or die;
printflush $P qq[
        unset key
        set xtics rotate by -45
        #set grid # vertical and horizontal grid lines
        set grid xtics # vertical grid lines only
        plot "$N" with lines lw 3
];
<STDIN>;
close $P;
__END__
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Update: rotating the text is tricky in that some of the terminals (output drivers of gnuplot) does not support it, or only supports rotating by multiples of right angles. This may also depend on the version of gnuplot you have. Rotating the text by any angle does work in at least the postscript driver though.