Is there an issue if a passport is within a year of expiring?

No.

Might be a problem if your passport has than 180 days.

LINK

6 months

Not to split hairs,
The officer at INM will almost always mark 180 (maximum) on your FMM form in the space indicated "dias" unless you present a Visa.
Even thought the website says 6 months, the officers computer displays the number of days between two dates. So be aware of your dates.