not quite. Consider:

use strict;
use warnings;

my $foo = undef;
my $bar = undef;

$foo += 1;
$bar = $bar + 1;
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Generates the warning:

Use of uninitialized value in addition (+) at noname1.pl line 8.
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Note that it is the $bar line only that generates the warning. The update assignment operators do not generate an uninitialized value warning when the left hand side is undefined, but the other non-boolean binary operators do. See perlsyn Declarations.