Preliminary lockout test good. Running sce-update -a in first terminal window, open another to run sce-import:
tc@box:~$ sce-import
Another SCE utility is presently in use, exiting..
Haen't tried the other way around yet, will report any issues otherwise probably good.
Another counter-productive command worthy of lock-out during import or update might be sce-debpurge -a .
[edit] Worked well the other way around too, thanks.