In docbook2fo.xsl in the template <xsl: template match = "docbook: listitem" mode = "ol">

there is just <xsl: number />
there should be:
<xsl:number />
<xsl:number format="i. " />
<xsl:number format="I. " />
<xsl:number format="A. " />
<xsl:number format="a. " />
depending on the type of list