PPaint (68k version) works on MorphOS, but there might be some setting which causes problems. Check PPaint/PPaint_Prefs/Startup_1.set file and if you have line
BLITLIBS = "personal_agnus_blit.library", "personal_68000_blit.library", 1
edit it with text editor and replace the 1 with 0.
@Jose
If you need 8 bit editing, then it just rules and is better than IFX for that

. For example if you need gif animations to web pages or if you're coding something for classic Amiga etc. PPaint just has almost tooo easy palette merging and editing functions. It's also good for every pixel perfect editing like icon/gadget/texture/everything editing if you don't need them in full color.