No. Math and especially numbers are not just symbol manipulation. Geometry is a counter-example. So is multiplication, for that matter.

Maybe you could say that algebra is just symbol manipulation.

And in any case - "set of rules" is exactly what transformers aren't good at. Transformers are good at capturing the essence of what you meant and responding in a sensible, but not rule-bound way. This works well for language problems.

Perhaps you could argue that transformers are just a set of rules (weights/parameters) being applied, and you might similarly argue that numbers reduce to logical symbols like S(0), S(S(0)), but then I'd argue that you're missing the point.