nope FF - the ban on numbers under wetsuits is either a national federation ban (Germany for example don't allow them but BTF don't have a specific rule on it), or event specific as a special rule (but I can't think of a UK one that bans them). WTC don't have a specific rule but I believe they adopt the country federation rule on this in whatever country the event is held in.
however, as SLAW says, best to check with the event race director.
TriSpirit always have aquabike races at their events (Brett Ashford and Owler) and they are well appreciated by those who do them either as they don't want to do the run or are injured or no longer capable of distance running (borked knees etc).
I personally think they are a good idea and it's easy to have them running alongside a full tri.
a few off road rides would help get your handling skills back to par (quite a few do Xterra with no or little off road experience), and understand how to see ahead and make sure your gear changes are appropriate for the upcoming section. sometimes you get little notice of what's ahead so you need to be ready. if you have any local rides in woods/forests that would help more than doing open trail rides.