Some things I've experienced over the years:
The ksh provided by redhat is pretty good nowadays. pdksh is/was less good. ksh has print statement bash does not.
If you have a requirement to print then lp/lpr/cups need a thorough checking over.
The Solaris grep/awk commands can be an issue.
Even if you decide on using ksh, the bash provided with redhat has a nice little known feature flag --rpm-requires that you can use to analyse a script:
$ bash --rpm-requires conman
So now we know what commands this script needs to execute. If you run it against your catalog of scripts you can quickly work out how many are using awk/sed etc.
Make sure that you check over any ulimit settings that are in solaris
Check solaris /etc/system file for semaphores/shared memory settings and check the appropriate settings can be made in linux sysctl.
/var/adm (Solaris) and /var/log (Linux)
Endianness - If you are migrating data/binary files between the systems then you need to make sure that any endian conversion has been taken care of, Sparc is big-endian, Intel little-endian.