Yes, no, and maybe.
There are threads where people actively search for recommendations on posts to merit, going there and suggesting posts (even if they are your own) is alright, it's even wanted. I dont see harm in it.
Another case would it be when you are sending unsolicited PMs to people who you suspect to have big amounts of sMerit. Here it should be 100% not allowed. Aggressive begging cant be tolerated.
When it comes to a post/thread, imo it depends on the content of it. Some threads currently ask for donations, and that's OK. They could ask for merit donations instead of BTC donations, I would find that OK.
Some threads have avertisements, and that's Ok, similar situation. This does not apply to all threads/posts alike, I think it's something everyone has to determine for themselve individually. Find your own line.