Ive had Hamps for ten years and the simple answer is yes they can be mated now assuming they are fertile.
If they were mine I would hold on though and mate them to lamb in december,that way you will be able to get them back in lamb under normal circumstances the following year.If they lamb in July this year you are going to put a real demand on your ewes if you want to tup them in say Oct /Nov the following season.
Ask your self what you are trying to achieve if it is economic and you dont want ewes hanging around doing anything then sell them now as cull ewes and buy some in lamb ewes.If your not bothered let them have a restful summer ,dont let them get two fat and mate them from July on wardwards.
I ve lambed hamps at various times of the year and without doubt ( and dependent on the weather) they do best lambing in mid feb to mid march
If you have not got a tup and are not wanting to keep the lambs pure get a charrollais,they make outstanding cossbred lambs and good replacements if you want to keep some back