Thanks for all the suggestions. Finally I find the reason for failing. It is alias issue on X64 bit connecting to 32 bit.
Initially I created on only Alias under SQL Native Client Configuration(32 bit) . Because of this SSIS package is running fine with DTEXECUI .
Where as sql job or XP_cmdshell looks for alias under sql native client for 64 bit.
after adding alias under 64 bit, SSIS package is running fine on both DTEXECUI & dtexec and in query window also.
I fell main reason is name resolution issue: some components looks for alias under 32 bit & few looks under 64 bit. Adding alias under both 32 & 64 bit resolved this problem .