Can i use fresh air concept in fcu?

yes can be done but it has to be noted that it may not achieve the humidification or dehumidification since there are some limitations for the FCU.

yes it can be employed usually we employ this system in case of small villa since the cost of fahu would be too high .keep in mind to consider the unit with the percentage of fresh air used remember to feed with fresh air fcu in corridor area 

Yes It should be used for a healthy indoor air quality

Yes, Definitely you can add fresh air to the FCU.

At our project we have added fresh air coming from the fresh air handler unit(FAHU) to the return plenum of FCU.

In most cases fresh air is delivered to the rear of the fan coil unit, Which mixes this air with the re-circulated air from the space and delivers it to the room, the benefit being that that the fresh air is conditioned before it is delivered

You can use Fresh Air in FCU, provided that FCU coil selection is done considering load of Fresh Air. But FA must be connected with RA Plenum or near RA inlet otherwise there will be humidity inside the False Ceiling that will cause Fungus.