I figured it out after some research. I'd still be curious to know how to NOT have to center if the marker is visible on the map.
var centerpoint = new google.maps.LatLng(lat_value, long_value);
edit: Found answer to how to not center map every time.
Pseudo code version.
1. Get values from Gmaps4Rails.map.getBounds().
2. Use resulting ta and la values to see if the marker is within those values.
3. If marker is outside of those values, center map, otherwise place marker without centering map.