Parâmetros Bash não são expressões regulares, são globs. Use:
$ zip /var/www/html/db-$(date +\%F-\%T).zip /var/www/html/db-*.sql
Do manual de bash
, em "Correspondência de padrões":
*
Matches any string, including the null string. When theglobstar
shell option is enabled, and*
is used in a pathname expansion context, two adjacent*
s used as a single pattern will match all files and zero or more directories and subdirectories. If followed by a/
, two adjacent*
s will match only directories and subdirectories.