I think the UT3Converter did have an option to convert such items as well.
You should check with Bl1tz on here.
He did a few map conversions with that tool. Perhapd he can tell you if you can use it for skin/model conversions as well
ohh...sorry but i think it was only converting maps (BSP,SMeshes,botpathing and lights...)...and only a few options for UT99...i have some special versions of the tool that XTremXP sended to me for my UT99 maps but it have no more options except the bsp rescaling if i remember well