It seems like John Lovelady also didn't have any major characters. Heck, even in the first season, Jerry Nelson had more characters than John Lovelady. Jerry nelson would often perform many characters per epsiode, both regular, semi-regular, irregular, or one-shot, while john Lovelady would often be stuck performing background characters, right hands, and characters who had their vocies dubbed later. He would normally perform a significantly small number of characters that he actually voiced.
To compare regular first season characters, Jerry nelson had Floyd, Robin (who only had one significant role during the first season), Vendaface (who was only in three eisodes near the end of the last season), one of the houses, the Shouting lady, all of the shouting ladys dance partners, Miss Mousey (who only had one significant role in the first season), Uncle Deadley, and Thog (who only appeared in three first season epsiodes, and only spoke in two of them). he also sometimes performed paul (from the jugband) and baskerville, though others have also voiced them.
John Lovelady had Crazy Harry, Nigel the Conductor, one of the houses, and the veterinarians hospital announcer, all characters who only appeared every once in awhile. John also occassionally performed some frogs and rats (he seems to have performed the most rats during the first season). Crazy harry and the announcer were both taken over by Jerry nelson, though they weren't any more or less major in the first season than in the later seasons (and how do we know that the first season announcer was supposed to be the same one in all season?). Jim Henson originally performed Nigel, and I'm not sure why he stopped performing him. Nigel also seems like the kind of character who could have easily had his own backstage plots, or at least some major backstage involvement. However, John Lovelady didn't perform him in any vocal roles untill really late in the first season, and all of those lines were really small.
Also, while it's been said in the epsiode guide at Muppet Central that John Lovelady had a good singing voice, he didn't have any characters in The Gogalala Jubilee Jugband (or at least he never voiced any members) or The Electric Mayhem (though Richard Hunt, who's probably better known for having a great singing voice, didn't have any members of his own untill the second season).
There are many roels that John Lovelady could have performed, such as any of the roles that Peter Friedman performed (though I also think that Jerry nelson could have performed Andre the Artist or the lead-singign raggmopp).