Here is my sample code which works with BPXWUNIX and uses the /etc/profile but I can see no way to get the users .profile to be included. As you can see the login flag is set (that is the 1 at the end of the bpxwunix parameter string.
/* rexx */
/* pass as an argument any OMVS command (i.e. env) */
parse arg cmd
/* now get the users home (pwd) location */
address syscall 'getpwnam' sysvar('sysuid') 'h.'
/* place into the environment stem as HOME */
env.1 = 'HOME='h.4
env.0 = 1
/* echo out the home and full command now */
say 'home:' env.1
say 'cmd:' cmd
/* issue the bpxwunix call */
x = bpxwunix(cmd,,s.,e.,env.,1)
/* view the results */
call stemedit 'view','s.'
call stemedit 'view','e.'
I'm using stemedit from www.cbttape.org file 895 to view the stdout and stderr stems.
This is a working answer: