Shouldn't be any kind of a problem. The old roses were probably same stock... that is, they were not hybrids but grew only on their own roots. You could check and see if there was any kind of "knob" where the graft would have been. The only reason for that concern is that true old roses are not susceptible to Black Spot the way new hybrid tea roses are. If there had been a tea or floribunda in that place before, I would suggest using some "dormant oil" next spring as soon as the weather warms a bit. This will keep any Black Spot from reoccuring...