In the UK, Ts tend to be less happy about their clients seeing more than one from what I can gather, some even contract against it (mine does actually, but he says there can be exceptions). It might be that your T would be fine with it, but it's not that common in this country I don't think.
That said, I tend to agree with something stopdog once said on this subject when I was contemplating taking on another T, which was that the therapist should have no say over what the client does outside of the therapy hour they are paid for.