In general, a full-time member of a project will be better than a part-time member. The main challenge is domain knowledge and communication.
As a part-time employee, you may feel more left out from the team. The other members of the team will know details about the project that you missed because you were out when the announcement was made.
In addition, a part-time employee may have more trouble being productive, as it sometimes takes time to get into a rhythm, and there is just less time to devote.
If you have more resources on the project to make up the difference, you'll have to remember that there are still more communication paths to consider, different skill sets, and more distributed domain knowledge.
On the contrary, if the project involves many different skill sets where there isn't enough for FTE (full time equivalent) work for someone with that skill set, then that may justify part-time workers. Just remember that communication will be more of a challenge.