I would assume, althought not completely sure, that bash is compatible with ksh ( only in this direction, not the other way ).
What will be most likely the problem is the usage of external programs. Since HP-UX is a lot different to the linux environment, there could be a lot of change required, especially these kinds:
- Some path names are different, hardcoded path names for programs will probably have to be changed
- External commands have to partially be changed
- invocation of commands with their options and switches are different and have to be adapted
The question to me is, if this is a onetime process or an extension, so that the scripts will run on both platforms in future. For the latter more work is required, to implement some kind of portability layer into all scripts.
Regarding automation, there is nothing I know of. I doubt that there is much regarding the fact that the issue is not to convert ksh syntax but a lot of external program calls, which is no question of converting one defined set of programming language syntax into another(like converting a perl script into c-code, which is possible and where converters exist), but a lot of arbitrary, non-standardized, redundant, ad-hoc code.
See also:
Bash / ksh - Portability Issues