Yes, you can use Leaflet Maps Marker and Maps Marker Pro within a commercial context. Anyway it is required that the attribution links for the licence conditions of the used maps don´t get removed from each map shown through the plugin on your website.
Maps Marker Pro is not licensed under GPL 2.0 but can of course also be used within a commercial context. The pro version also allows you to remove the backlinks to MapsMarker.com – please check out the terms of service for more details.
Depending on geocoding or basemap providers which require additional registration, additional requirements may apply, please check the ToS of the external providers before signup for more details.