yeah, i think it is considered abusing the hoplink system & your account may be terminated without notice..that`s what happened to my friend!! but there are many who would tell you that it`s allowed. anyway, just a warning about using third party link shrinking services. I would recommend these for email marketing as a last resort, but getting your own domain then forwarding and masking it is the ideal solution.
I prefer zzd.in, its from someone on this forum cant remember who. Its short though and lets you make your url whatever you want.