Multiple 30A outlets on the same breaker
No, as long as you don't overload the circuit of course

This is stated most clearly in NEC 210.23(B):


  210.23 Permissible Loads, Multiple-Outlet Branch Circuits. In no case shall the load exceed the branch-circuit
  ampere rating. A branch circuit supplying two or more outlets or receptacles shall supply only the loads specified
  according to its size as specified in 210.23(A) through (D)
  and as summarized in 210.24 and Table 210.24.


...


  (B) 30-Ampere Branch Circuits. A 30-ampere branch circuit shall be permitted to supply fixed lighting units with
  heavy-duty lampholders in other than a dwelling unit(s) or
  utilization equipment in any occupancy. A rating of any one
  cord-and-plug-connected utilization equipment shall not
  exceed 80 percent of the branch-circuit ampere rating.