Or a simple Perl one-liner:

$ echo '
james     yes
dave      yes
mike      yes
ken       no
jon       yes
jon       no
ken       yes
jon       yes
mike      no
james      yes
dave      yes
mike      no
ken       no
jon       yes
jon       yes
' | perl -nE 'my ($name, $val) = split; $hash{$name} ++ if $val eq "ye
+s"; END{ say "$_\t$hash{$_}" for keys %hash}'
james   2
mike    1
dave    2
jon     4
ken     1
[download]

I realize that you spoke about col5, but I had to use the data as you supplied it. If the flag is really in col5 (i.e. presumably field subscript 4), change the one-liner to:

perl -nE 'my ($name, $val) = (split)[0,4]; $hash{$name} ++ if $val eq 
+"yes"; END{ say "$_\t$hash{$_}" for keys %hash}'
[download]