Well, it seems that including partial FSU kit hasn't hurt things in the past. The 2007 contest had over 100 entries for all-FSU, and 40+ for hybrid kit. The idea is to encourage participation and have some fun. I remember last year feeling rather excluded when I asked if I could use my IIIf and FSU glass and was knocked back.
In a sense, this is a bit like one of those 'show your pictures taken with X bit of equipment' threads, but in the context of a friendly contest. It's as much about putting the equipment to use and seeing what can be done with it as it is about the actual pictures themselves. Were it otherwise, there would be no FSU contest at all.
FSU glass on non-FSU bodies is a notably popular combination - I would never have gotten into FSU gear if I hadn't bought a J-12 and turrent finder for my IIIf to try out the 35mm focal length. Followed by a J-3 for the wide aperture stuff, followed by a rush purchase of a FED 1 for last year's contest (which lasted two rolls before the curtain slid off the drum), followed by a J-8 to convert a pre-war Sonnar to LTM, which had a Zorki 4 attached to it, followed by another J-8, and a set of 6 FSU B&W filters. I've been window shopping for J-11s lately, even though I don't really use long lenses - curious to see what I do with a 135 on a ranegfinder.
The contest raises awareness of the equipment and encourages people to try it. For many, it starts with one FSU lens on a non-FSU body, and I don't think there is much to be gained from not inviting them to have a go. For those that don't have any FSU kit, it also keeps the cost of entry down - a J-8 or I-61 is a cheap start.