Hello! I think it depends in the modding tool/game engine you're using.
With SF1 editor, nope, not possible.
With sf2 tools (which have a wider variety) I wouldnt be completely sure, you'd have to check on the disasm web page, maybe disasm can do it, but I wouldn't count on it.
On a completely...
Based on my recent research about enemies in the sf world not available in SF1-like graphics, I have the following:
Treant * (sitd)
Mandragora * * (sitd)
Ghost Armor * (sitd)
Chest Mimic (sitd)
Ninja * (sf3)
Samurai * * (present in the force side only)
Yes, I totally recommend Suikoden and Suikoden 2 as sprites sources (available in The Spriters Resource).
For this one in particular, I didn't use resizing, it was kinda medium sized, and adding the sword made it big enough.
If you're going to port Suikoden assets, you might want to ask me...