Some will rightly point out that you cannot be a Buddhist and a Catholic at the same time! However, yoga is not necessarily anti-Christian and practising it does not necessarily mean taking part in Buddhist meditation. As with so many other things in our secular society, its down to the individual to use their own judgement as to whether and to what extent a particular service or practice is compatible with the Faith. Some Yoga groups I would not go near as I know they are conversion to Buddhism courses (many quite overtly and honestly so). I myself have found that the kind of Yoga practised by Birthlight was compatible with the Faith, focussed as it was on relaxation and  physical development. On the one occasion I felt uncomfortable with an exercise (salute to the Sun) I just sat out and no one minded at all.