there are bh and wh 301 redirects,
anything made to manipulate the SERPs is considered bh, that including buying a good clean expired domain and redirecting to yours,
while in fact, google would never know if it's an old one of yours (genuine redirect) or bought one,
what you should stay away from is the spam not bh stuff, decent made bh stuff does work and will always work,
simply avoid anything that could be spotted and especially the easily spotted ones,
if you pick one good niche & language relevant domain and redirect it to your website with all of the top pages, then it will work like a charm,
On the other hand, redirecting a bunch of them aggressively will be easily spoted and wouldn't simply work