Linear image sensor output signal processing
Processing the TCD1103 output signal


You can certainly buffer the OS output signal with an opamp, but for the  LMH6658 you can't power the opamp from the 3.3V supply used for the TCD1103.

The OS signal dark level is very close to 3.3V so you need to be able to handle this as the CM signal for the opamp.
The LMH6658 CM minimum is not characterized for a 3.3V supply but at a 5V supply it is limited to 2.8V worst case. The ouptut votlage swing is also a problem for this opamp, but the input restrictions dominate. 



A better choice may be the OPA837/OPA2837 which has a CM minimum of 3.7V for a 5V supply. 



For either opamp choice you would still need to use higher supply voltage to allow the OS signal to be correctly buffered.
For the LMH6658 I'd suggest a minimum 6V supply.
For the OPA837 you could use a 5V supply (which you may already have). 

Update:
From your datasheet you can see the OS output signal is high (close to 3.3V) for Dark:
 

SS = Ground. 
The Dark voltage level output is specified as an absolute value (but it's from an inverted perspective).    

The datasheet also shows that the OS outpur is a negative going signal (much like you might expect from a video signal) from whatever the OS high level is.