Finally I managed to run ecw plugin inside geoserver version 2.7.2
Downloaded libecw source from http://meuk.technokrat.nl/libecwj2-3.3-2006-09-06.zip
Applied this patch https://github.com/makinacorpus/libecw/blob/master/Source/C/NCSUtil/NCSPrefsXML.cpp.rej
Ran ./configure, make and sudo make install commands to build.
Override generated libs over image-io-ext libs. Make sure the path to the newly compiled .so's are in the LD_LIBRARY_PATH environment variable before the existing ones (present in geoserver gdal documentation).
The other steps told in geoserver gdal documentation (cant post more than 2 links) are valid.
