Defining IDENTPROTO neither includes nor excludes RFC1413 code. All it does is change the default value for the Timeout.ident option (See this section):

APPENDDEF(`confENVDEF', `-DIDENTPROTO=0') set Timeout.ident=0 by default
APPENDDEF(`confENVDEF', `-DIDENTPROTO=1') set Timeout.ident=30 by default

If you are running a precompiled sendmail binary, you can use the -d0.10 debugging command-line switch (-d0.10) to determine if IDENTPROTO support is defined (if it appears in the list, it is set to 1). New ports should be reported to sendmail@sendmail.org so that they can be folded into future releases.